MIPS64: Added checks for dissasembled instructions in MIPS64r6 in cctests.

TEST=cctests/test-dissasm-mips64

Conflicts:
	test/cctest/test-disasm-mips64.cc
MIPS64: Fixed cctest for dissasembler and assembler when running on MIPS64r6 ISA.
Dissasembler test is also checking new/updated instructions, and assembler test for unaligned load/store is skipped.

TEST=cctest/test-disasm-mips64,test-assembler-mips64