target/mips: Rename MMI-related opcodes

Rename MMI-related opcodes.
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: NStefan Markovic <smarkovic@wavecomp.com>
Signed-off-by: NAleksandar Markovic <amarkovic@wavecomp.com>