MIPS64: Fix loading constants with li() macro.

Added new test.

TEST=cctest/test-macro-assembler-mips64/LoadConstants
BUG=
MIPS64: Add a cast to TEST(LoadConstants) to make Mentor compiler happy.

Compiling with mentor gcc 4.8.1 failed when passing array pointer thru
CALL_GENERATED_CODE macro. Simple cast fixes it.

Also fixed un-related too-long line.
MIPS64: Fixes Math.pow() error for edge cases.

MathPow Stub expected signed extended input.
The test fails for pow(+Infinity,-1).

TEST=test262/S15.8.2.13_A12
MIPS64: Add missing instructions for conversion to mips64 simulator.

TEST=
MIPS64: Fixed cctests for assembler and simulator.

Fixed ADDU, ADDIU, SUBU and LUI to sign-extend result.
Fixed warnings on compiling cctest.
Fixed style issues.

TEST=cctest/test-assembler-mips64.cc/MIPS2, MIPS11, MIPS16