arm64/vfp: Get rid of READ/WRITE_SYSREG32

arm64/vfp: Get rid of READ/WRITE_SYSREG32

AArch64 registers are 64bit whereas AArch32 registers
are 32bit or 64bit. MSR/MRS are expecting 64bit values thus
we should get rid of helpers READ/WRITE_SYSREG32
in favour of using READ/WRITE_SYSREG.
We should also use register_t type when reading sysregs
which can correspond to uint64_t or uint32_t.
Even though many AArch64 registers have upper 32bit reserved
it does not mean that they can't be widen in the future.

Modify type of FPCR, FPSR, FPEXC32_EL2 to register_t.

Signed-off-by: Michal Orzel <michal.orzel@arm.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>