KVM: MIPS: Allow multiple VCPUs to be created

Increase the maximum number of MIPS KVM VCPUs to 8, and implement the
KVM_CAP_NR_VCPUS and KVM_CAP_MAX_CPUS capabilities which expose the
recommended and maximum number of VCPUs to userland. The previous
maximum of 1 didn't allow for any form of SMP guests.

We calculate the values similarly to ARM, recommending as many VCPUs as
there are CPUs online in the system. This will allow userland to know
how many VCPUs it is possible to create.

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