crypto: vmx - convert to SPDX license identifiers

Remove the boilerplate license text and replace it with the equivalent
SPDX license identifier.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>