MIPS64: Optimize address loading in li() macro to use less instructions.

The optimization relies on the fact that on 64-bit systems (x64, mips64) only
first 48 bits that contain complete information of address are used.

Fixed all code patching sites accordingly.

New test cctest/test-macro-assembler-mips64/LoadAddress added.
Merge remote-tracking branch 'mrb/dm-mips64' into mips64-gbl-merge

Conflicts (fixed):
	src/mips64/assembler-mips64-inl.h
	src/mips64/assembler-mips64.cc
	src/mips64/codegen-mips64.cc
	src/mips64/debug-mips64.cc
	src/mips64/lithium-codegen-mips64.cc
	src/mips64/macro-assembler-mips64.cc