Convert license tags to SPDX

Also clarifies provenance of code in `apps/fdtgen/fdt_utils.c`

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

Rexpand licenses

Licenses: s/NICTA_BSD/DATA61_BSD

Unexpand licenses

Replace seL4RPC with seL4RPCCall

In order to make the CAmkES repo work with the new-rt kernel,
we update all seL4RPC connectors to be seL4RPCCall.

The reason for this is that we haven't updated the seL4RPC connector
templates, since they are going to be deprecated soon, ostensibly.

Since we don't want all the CAmkES examples to just not work on the
new-rt kernel, we just update all the examples to use seL4RPCCall right
now.

Fix licence headers.

Initial import of example applications.

The original port of these example applications from the 'master' branch of
CAmkES was done in https://github.inside.nicta.com.au/mfernandez/project.