KVM: MIPS: Enable KVM support for Loongson-3

This patch enable KVM support for Loongson-3 by selecting HAVE_KVM, but
only enable KVM/VZ on Loongson-3A R4+ (because VZ of early processors
are incomplete). Besides, Loongson-3 support SMP guests, so we clear the
linked load bit of LLAddr in kvm_vz_vcpu_load() if the guest has more
than one VCPUs.

Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Reviewed-by: Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>
Signed-off-by: Huacai Chen <chenhc@lemote.com>
Co-developed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Message-Id: <1590220602-3547-15-git-send-email-chenhc@lemote.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>