MAINTAINERS: Add KVM for MIPS entry

I've pretty much been maintaining KVM for MIPS for a while now. Lets
make it more official (and make sure I get Cc'd on relevant patches).

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/11898/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>