arch, base: Move arm AtomicOpFunctor into the generic header

arch, base: Move arm AtomicOpFunctor into the generic header

These AtomicGenericxOp functors are not arm specific:
They just define a set of different functors depending
on the number of operands they are using.

Change-Id: Ida75066823c7718aee05717194cdb8225b700c5d
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23564
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>