[mips][mips64r6] Set ELF e_flags for MIPS32r6/MIPS64r6. Also do MIPS-I to MIPS-V

Differential Revision: http://reviews.llvm.org/D4386


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212346 91177308-0d34-0410-b5e6-96231b3b80d8