MIPS: generic: Enable crc32-mips on r6 configs

Enable the crc32-mips module on MIPS generic r6 configs, where the
required MIPS r6 CRC instructions may be available.

As well as allowing the CRC instructions to be utilised, this should
also ensure the module gets some build coverage.

Signed-off-by: James Hogan <jhogan@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Marcin Nowakowski <marcin.nowakowski@mips.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/18602/