MIPS: Add functions for hypervisor call

Introduce kvm_hypercall[0-3].
Define three new hypercalls for MIPS: GET_CLOCK_FREQ, EXIT_VM, and
CONSOLE_OUTPUT.

[andreas.herrmann:
  * Properly define hypercalls and HC numbers for MIPS
    in kvm_para.h header files]

Signed-off-by: David Daney <david.daney@cavium.com>
Signed-off-by: Andreas Herrmann <andreas.herrmann@caviumnetworks.com>
Cc: linux-mips@linux-mips.org
Cc: James Hogan <james.hogan@imgtec.com>
Cc: kvm@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/7005/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>