crypto: crc32 - Rename generic implementation

The generic crc32 implementation is currently called crc32.  This
is a problem because it clashes with the lib implementation of crc32.

This patch renames the crypto crc32 to crc32_generic so that it is
consistent with crc32c.  An alias for the driver is also added.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>