kernel & addons: Build with the non-legacy GCC even on x86_gcc2h.

Only one code change: for some reason, GCC chokes on the cr3 functions
as macros (throwing errors about invalid registers.) The BSDs have them
as inline functions instead, so they are converted to that here.

Tested and working. There seems to be about a 10% decrease in CPU time
on some compilation benchmarks that I briefly tried.

Change-Id: I31666297394d7619f83fca6ff5f933ddd6f07420
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4515
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

efi: Refactor CPU code to be arch-specific

* Migrate some platform agnostic architecture code into
boot/arch from efi/arch. This helps to avoid conflicts
between kernel and boot sources as well.
* Conflicts between arch_cpu in efi and kernel code means
bootcode really should *never* directly use kernel arch
headers. (other platforms don't, which is why they don't
have this same issue)
* We carefully thread any needed kernel headers (namely
assembly helper macros) into the bootloader headers without
mixing in the whole conflicting kernel/arch headers.
* ARM now properly get its cpu init code called, and we
progress further into the EFI bootloader.

Change-Id: If67ec9758b5ce68563ebd9eb45d5196401911c67
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2975
Reviewed-by: waddlesplash <waddlesplash@gmail.com>