Vector Integer Negate Instructions:

vnegw: Vector Negate Word
vnegd: Vector Negate Doubleword
Signed-off-by: NNikunj A Dadhania <nikunj@linux.vnet.ibm.com>
Reviewed-by: NThomas Huth <thuth@redhat.com>
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>