[MIPS64] Emulate MSA branch instructions

This patch adds MSA branch instruction emulation for MIPS64.

Reviewers: tberghammer, jaydeep
Subscribers: tberghammer, lldb-commits, nitesh.jain, mohit.bhakkad (Mohit Bhakkad), bhushan (Bhushan Attarde)
Differential: http://reviews.llvm.org/D12356
llvm-svn: 246745