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

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

Move the powerpc-optimized CRC code from arch/powerpc/lib/crc* into its
new location in lib/crc/powerpc/, 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/20250607200454.73587-8-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>