arm64: fpsimd: Correctly annotate exception helpers called from asm

A couple of FPSIMD exception handling functions that are called
from entry.S are currently not annotated as such.

This is not a big deal since asmlinkage does nothing on arm/arm64,
but fixing the annotations is more consistent and may help avoid
future surprises.

This patch adds appropriate asmlinkage annotations for
do_fpsimd_acc() and do_fpsimd_exc().

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>