[POWERPC64BE] mrsas: add big-endian support
Add endiannes conversions in order to support big-endian platforms
Submitted by: Andre Fernando da Silva <andre.silva@eldorado.org.br>
Reviewed by: luporl, alfredo, kadesai (on email)
Sponsored by: Eldorado Research Institute (eldorado.org.br)
Differential Revision: https://reviews.freebsd.org/D26531