crypto: vmx - Adding enable_kernel_vsx() to access VSX instructions

vmx-crypto driver make use of some VSX instructions which are
only available if VSX is enabled. Running in cases where VSX
are not enabled vmx-crypto fails in a VSX exception.

In order to fix this enable_kernel_vsx() was added to turn on
VSX instructions for vmx-crypto.

Signed-off-by: Leonidas S. Barbosa <leosilva@linux.vnet.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>