MIPS64: Fix for fmt, shouldn't be shifted in cmp.
MIPS64: Fix for the instruction type for BC1EQZ, BC1NEZ.
MIPS64: Fixed a few bugs, removed asserts.
MIPS64: Fix fmt, use L instead D in test-assembler-mips64.cc.
MIPS64: Added BC1EQZ, BC1NEZ to IsBranch.
MIPS64: Added instructions for MIPS64r6, and implemented previously added to dissasembler.

TEST=
MIPS64: Added branch compact instructions to assembler and dissasembler which were ambiguous from specification.

TEST=
MIPS64: Skip disassembler test for Mul/div/mod r6 instructions.
MIPS64: Add cmp.d instruction in disassembler and fix dsll/dmul/dmulh opcode overlapping.

TEST=
BUG=
Merge branch 'mips64-gbl' of github.com:paul99/v8m-rb into mips64-gbl

Conflicts:
	src/mips64/disasm-mips64.cc
	test/cctest/test-disasm-mips64.cc
MIPS64: Added checks for instructions in MIPS64r6.

TEST=cctests/test-dissasm-mips64