MIPS64: Fix LCodeGen::DoFlooringDivByPowerOf2I() and MacroAssembler::TruncatingDiv().

TEST: mjsunit/compiler/division-by-constant
MIPS64: Fix DoLoadKeyedFixedArray() and DoStoreKeyedFixedArray().

TEST: mjsunit/array-iteration mjsunit/array-indexing etc.. (debug mode).