[mips][mips64r6] Add addiupc, aluipc, and auipc

Summary:
No support for symbols in place of the immediate yet since it requires new
relocations.

Depends on D3671

Reviewers: jkolek, zoran.jovanovic, vmedic

Reviewed By: vmedic

Differential Revision: http://reviews.llvm.org/D3689