arm64: lib: Consistently enable crc32 extension

Currently most of the assembly files that use architecture extensions
enable them using the .arch directive but crc32.S uses .cpu instead. Move
that over to .arch for consistency.

Signed-off-by: Mark Brown <broonie@kernel.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20200414182843.31664-1-broonie@kernel.org


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