lib/crc: make the CPU feature static keys __ro_after_init

lib/crc: make the CPU feature static keys __ro_after_init

All of the CRC library's CPU feature static_keys are initialized by
initcalls and never change afterwards, so there's no need for them to be
in the regular .data section.  Put them in .data..ro_after_init instead.

Reviewed-by: "Martin K. Petersen" <martin.petersen@oracle.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Heiko Carstens <hca@linux.ibm.com> # s390
Link: https://lore.kernel.org/r/20250413154350.10819-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>