libsel4: fix license tags

These files should have been released under BSD-2-Clause in the first
place (as per parent LICENSE.md file).

Closes #245

Signed-off-by: Gerwin Klein <gerwin.klein@data61.csiro.au>

Enabled IPC debug features under new config

Introduced a new config flag to enable
userError format strings to be written to the IPC buffer.
Another config bool has been introduced to toggle
printing the error out and this can also be set at runtime.

Signed-off-by: Saer Debel <saer.debel@data61.csiro.au>

Convert license tags to SPDX identifiers

This commit also converts our own copyright headers to directly use
SPDX, but leaves all other copyright header intact, only adding the
SPDX ident. As far as possible this commit also merges multiple
Data61 copyright statements/headers into one for consistency.

mcs: scheduling context donation over ipc

After this commit, threads blocked on an endpoint can recieve a
scheduling context from the thread that wakes the blocked thread.

python2 --> python3

Update all scripts and build system to call python3, given python2's
upcoming doom. Use sys.maxsize instead of sys.maxint in one script
(maxint does not exist in python3).

style: use consistent styling for all cmake files

Add .cmake-format.yaml which defines custom functions with kwargs to
style nicely

cmake: use snake_case for RegisterDriver & CPPFile

Our upcoming cmake styling tool requires any custom functions you want
styled nicely to be lower case. We only need to style these two nicely,
as they have kwargs we would like aligned.

Rename shared_types*.bf files to be consistent

Now these bitfield definitions are generated from the same source file
in the kernel and libsel4, and also result in the same include path: <sel4/shared_types_gen.h>

libsel4: rename sel4_gen custom target to sel4_generated

add_config_library for sel4 adds sel4_Gen custom target. Having two targets with
names that only differ in case results in strange build problems on systems with
case insensitive file systems (I've seen it only on OS X but I assume Win is
affected too).

libsel4: remove unused extra_cflags

This is now unused due to the usage of CPPFile which allows us to just use the includes
via the `include_directories`

libsel4: Replace GenCPPCommand with CPPFile

CPPFile is a much more robust version of GenCPP command. We drop the `extra_cflags`
as the CPPFile command uses regular cmake compilation and will use the include
directories added by `include_directories`, which includes all the directories from
`extra_cflags`

libsel4: Provide includes directly to include_directories

include_directories makes these directories directly available to all compilation that
happens, without needing to provide additional target link directories. This is the
first step to removing the `extra_cflags` variable

cmake: Avoid placing lists in generator expressions

Placing lists directly in the generater expression means that this string, despite having
semicolons in it, is not actually a list, as it has an expression (the generator expression)
spanning multiple lists. This leads to confusion during argument processing and expansion

libsel4: Make guard and badge definitions mode specific

The definitions of guard and badge sizes is going to be changed for 64-bit platforms,
this change provides an easy way of providing different definitions

libsel4: Remove bitfield type unifying Guard and Badge construction

Using the bitfield generator to treat guards and badges as a union type can be convenient,
but it requires reserving a bit in the data for the bitfield run time type information.
This type information is not needed by the kernel as it knows implicitly whether the passed
data is a badge or a guard based on the kind of cap being operated on. However, with the
type information present we cannot pass a word sized piece of data to the kernel.

The solution here is to go back to using a plain seL4_Word as the type for invocations
that want a capdata and let the user either construct a badge as a plain word, or use
the seL4_CNode_CapData bitfield for constructing a guard, although they have to manually extract
the word representation out of it.

Add a CMake based build system

This commit adds an alternate build system using CMake that operates indepenently of
the existing Kconfig+Kbuild+make based build system