crypto: ghash-generic - move common definitions to a new header file

Move common values and types used by ghash-generic to a new header file
so drivers can directly use ghash-generic as a fallback implementation.

Fixes: cc333cd6 ("crypto: vmx - Adding GHASH routines for VMX module")
Cc: stable@vger.kernel.org
Signed-off-by: Marcelo Cerri <marcelo.cerri@canonical.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>