MIPS: Take in account load hazards for HI/LO restoring

MIPS CPUs usually have 1 to 4 cycles load hazards, thus doing load
and right after move to HI/LO will usually stall the pipeline for
significant amount of time. Let's take it into account and separate
loads and mthi/lo in instruction sequence.

The patch uses t6 and t7 registers as temporaries in addition to t8.

The patch tries to deal with SmartMIPS, but I know little about and
haven't tested it.

Changes in v2:
- clear separation of actions for SmartMIPS and pre-MIPSR6.

Signed-off-by: Siarhei Volkau <lis8215@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>