lib/crc: Move polynomial definition to separate header

Allow other drivers and parts of kernel to use the same define for
CRC32 polynomial, instead of duplicating it in many places.  This code
does not bring any functional changes, except moving existing code.

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