[MIPS] Support SNI RM200C SNI in big endian mode and R5000 processors.

Added support for RM200C machines with big endian firmware
Added support for RM200-C40 (R5000 support)
    
Signed-off-by: Florian Lohoff <flo@rfc822.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>