stxvb16x: Store VSX Vector Byte*16

Vector (8-bit elements):
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|F0|F1|F2|F3|F4|F5|F6|F7|E0|E1|E2|E3|E4|E5|E6|E7|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

Store results in following:

Little/Big-endian Storage
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|F0|F1|F2|F3|F4|F5|F6|F7|E0|E1|E2|E3|E4|E5|E6|E7|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Signed-off-by: NNikunj A Dadhania <nikunj@linux.vnet.ibm.com>
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>