MIPS: KVM: Convert emulation to use asm/inst.h

Convert various MIPS KVM guest instruction emulation functions to decode
instructions (and encode translations) using the union mips_instruction
and related enumerations in asm/inst.h rather than #defines and
hardcoded values.

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