Merge tag 'soc2arch-immutable' into riscv-dt-for-next

SOC_FOO to ARCH_FOO conversion for RISC-V

RISC-V is an outlier in using SOC_FOO rather than ARCH_FOO for
vendors/micro-archs. SOC_FOO may make more sense (I personally prefer
it), but the rest of the "world" uses ARCH_FOO. That'd be fine, with
with an increasing number of existing SoC vendors moving to RISC-V,
unifying our symbol names with the expectations of the rest of the world
makes sense.
Folks did not seem keen on changing the world (and they can't really be
blamed for that) so convert RISC-V over to match.

Add some ARCH_FOO stubs alongside the existing SOC_FOO ones, which will
be removed once all users of SOC_FOO have been converted*, and convert
the DT bits of RISC-V kbuild over to the new symbols.

* It may be best to wait until after the next LTS to remove the SOC_FOO
  ones, for the sake of external users.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>