arch/arm: Allow ceph_crc32c_aarch64 to be chosen only if it is compiled in

arch/arm: Allow ceph_crc32c_aarch64 to be chosen only if it is compiled in

If the build host does not support the crc32cx instruction, HAVE_ARMV8_CRC will not be set and ceph_crc32c_aarch64 will be a dummy function that always returns zero. However, if HWCAP_CRC32 is supported on the actual target machine, that dummy function will be selected anyway. This patch ensures ceph_crc32c_aarch64 will never be chosen if it is not compiled in.

Fixes: https://tracker.ceph.com/issues/36030
Signed-off-by: David Wang <planetbeing@gmail.com>