* MIPS: replaced opcode mapping functions with array, much shorter that way. Separate "overflow" mapping is also no longer needed.
* Use SRAV/SRLV/SLLV opcodes for shifts by variable amount.


git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@25038 3ad0048d-3df7-0310-abae-a5850022a9f2