Distinguish KERNEL_ARCH_DIR from KERNEL_ARCH.

On x86_64, the KERNEL_ARCH should really be "x86_64", but it was "x86"
as the architecture sources/headers directory is shared between 32 and 64 bit.

Should not be a functional change on any platform outside x86_64.

sparc: boot mmu support

Get enough of the mmu working to be able to allocate memory.

Unlike on PowerPC, we get both address and size as 64bit values. So
adjust of_region to allow this.

Also unlike the PPC port, we do not drive the hardware directly, instead we
rely on the openboot primitives to manage the translation table. This
allows staying independant of the hardware, which is a good idea at
least for the bootloader (we can do actual hardware things in the
kernel)

Change-Id: Ifa57619d3a09b8f707e1f8640d8b4f71bb717e2a
Reviewed-on: https://review.haiku-os.org/c/haiku/+/1482
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>

openfirmware: fix jamfiles

Without the MultiArchDirSetup, these would not use the boot cflags, and
end up being compiled position-independant. Of course, the a.out format
does not allow relocations, so this could not work.

Change-Id: I6bb570e545f1533200511e6881f71feedb77025b
Reviewed-on: https://review.haiku-os.org/c/1481
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

sparc: fix openfirmware entry point.

According to the IEEE standard documentation, the OpenFirmware entry
point should be in %o3. But that doesn't work, and both FreeBSD and
NetBSD expect it in %o4 (5th argument of the function). I suspect this
was changed for 64bit sparc, but neither the sparc nor 64bit
openfirmware specs mention it.

Move the sparc and powerpc specific parts out of the generic start.cpp
for openfirmware as they each have some specificities. More
specifically:
- sparc already clears bss for us
- entry point arguments are different
- determine_machine is of course platform specific

Change-Id: Icaa05087e88ea4d29198e3565223459aed75cdf9
Reviewed-on: https://review.haiku-os.org/c/1470
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

sparc: fix bootloader build

- Add various missing jamfiles
- Add required implementation stubs
- Update openfirmware jamfiles for multiboot support
- Update linker rules for sparc loader

Change-Id: I2d06c7a4d33827f58d82946687003f9a0dcb1b7d
Reviewed-on: https://review.haiku-os.org/c/1329
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

sparc: add defines and minimum set of required files

Gets the stage0 bootstrap to run.
Imlementation is probably nonsense at this point.

Change-Id: I10876efbb54314b864c0ad951152757cdb2fd366
Reviewed-on: https://review.haiku-os.org/c/1061
Reviewed-by: waddlesplash <waddlesplash@gmail.com>