This patch makes the needed changes to the lxvw4x for Little Endian.
The data was being loaded in the Big Endian data order for most
cases.  The code in host_ppc_isel.c was changed to do a right
shift and to permute the hi and lo registers in the other order
to ensure the data was always loaded in BE order.  The lxvw4x
emulation in guest_ppc_toIR.c was changed to permute the data from
the BE order to LE order when running on an LE system.

bugzilla 339433

git-svn-id: svn://svn.valgrind.org/vex@2973 8f6e269a-dfd6-0310-a8e1-e2731360e62c