lib/crc: loongarch: Migrate optimized CRC code into lib/crc/

lib/crc: loongarch: Migrate optimized CRC code into lib/crc/

Move the loongarch-optimized CRC code from arch/loongarch/lib/crc* into
its new location in lib/crc/loongarch/, and wire it up in the new way.
This new way of organizing the CRC code eliminates the need to
artificially split the code for each CRC variant into separate arch and
generic modules, enabling better inlining and dead code elimination.
For more details, see "lib/crc: Prepare for arch-optimized code in
subdirs of lib/crc/".

Reviewed-by: "Martin K. Petersen" <martin.petersen@oracle.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Acked-by: "Jason A. Donenfeld" <Jason@zx2c4.com>
Link: https://lore.kernel.org/r/20250607200454.73587-6-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>