MIPS: uasm: Add MTHI/MTLO instructions

Add MTHI/MTLO instructions for writing to the hi & lo registers to uasm
so that KVM can use uasm for generating its entry point code at runtime.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>