Disable MSA optimization for big endian arch

The current upstreamed code has been written and tested for Little Endian systems.
We do have plans to add the Big Endian support in near future, but till that time, need to disable all to avoid its usage and failures.

Signed-off-by: Shivraj Patil <shivraj.patil@imgtec.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>