powerpc: Handle VSX alignment faults correctly in little-endian mode

This patch fixes the handling of VSX alignment faults in little-endian
mode (the current code assumes the processor is in big-endian mode).

The patch also makes the handlers clear the top 8 bytes of the register
when handling an 8 byte VSX load.

This is based on 2.6.32.

Signed-off-by: Neil Campbell <neilc@linux.vnet.ibm.com>
Cc: <stable@kernel.org>
Acked-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>