Add a CRC32 feature bit and wire it up to the CPU id register so we
will be able to use alternatives patching for CRC32 operations.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>