arm64/sysreg: Guard SYS_FIELD_ macros for asm

The SYS_FIELD_ macros are not safe for assembly contexts, move them inside
the guarded section.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220818213613.733091-3-broonie@kernel.org


Signed-off-by: Will Deacon <will@kernel.org>