crypto: vmac - Make VMAC work when blocks aren't aligned

VMAC implementation, as it is, does not work with blocks that
are not multiples of 128-bytes.  Furthermore, this is a problem
when using the implementation on scatterlists, even
when the complete plain text is 128-byte multiple, as the pieces
that get passed to vmac_update can be pretty much any size.

I also added test cases for unaligned blocks.

Signed-off-by: Salman Qazi <sqazi@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>