KVM: MIPS: let generic code call prepare_flush_shadow

mainline inclusion
from mainline-v5.13-rc1
commit 566a0bee
category: feature
bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I7S3VQ
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=566a0beef52c83f13b67aef02b2bc0aa63c0e0d6



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Since all calls to kvm_flush_remote_tlbs must be preceded by
kvm_mips_callbacks->prepare_flush_shadow, repurpose
kvm_arch_flush_remote_tlb to invoke it.  This makes it possible
to use the TLB flushing mechanism provided by the generic MMU
notifier code.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>