arm64/sve: Move read_zcr_features() out of cpufeature.h
Having read_zcr_features() inline in cpufeature.h results in that
header requiring #includes which make it hard to include
<asm/fpsimd.h> elsewhere without triggering header inclusion
cycles.
This is not a hot-path function and arguably should not be in
cpufeature.h in the first place, so this patch moves it to
fpsimd.c, compiled conditionally if CONFIG_ARM64_SVE=y.
This allows some SVE-related #includes to be dropped from
cpufeature.h, which will ease future maintenance.
A couple of missing #includes of <asm/fpsimd.h> are exposed by this
change under arch/arm64/. This patch adds the missing #includes as
necessary.