MIPS: KVM: Implement PRid CP0 register access

Implement access to the guest Processor Identification CP0 register
using the KVM_GET_ONE_REG and KVM_SET_ONE_REG ioctls. This allows the
owning process to modify and read back the value that is exposed to the
guest in this register.

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

diff --cc Documentation/virtual/kvm/api.txt
Simple merge

diff --cc arch/mips/include/asm/kvm_host.h
Simple merge

diff --cc arch/mips/kvm/mips.c
Simple merge