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=