KVM: x86/mmu: Zap SPTEs on MTRR update iff guest MTRRs are honored

When guest MTRRs are updated, zap SPTEs and do zap range calcluation if and
only if KVM's MMU is honoring guest MTRRs, which is the only time that KVM
incorporates the guest's MTRR type into the final memtype.

Suggested-by: Chao Gao <chao.gao@intel.com>
Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: Kai Huang <kai.huang@intel.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Link: https://lore.kernel.org/r/20230714065156.20375-1-yan.y.zhao@intel.com
[sean: rephrase shortlog]
Signed-off-by: Sean Christopherson <seanjc@google.com>