vmx: Fix vector loads on ppc64le

Use vector intrinsic for loading possibly unaligned data instead of a
typecast.

Bugzilla: https://bugzilla.redhat.com/1572540


Signed-off-by: Dan Horák <dan@danny.cz>
Signed-off-by: Adam Jackson <ajax@redhat.com>
Tested-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>