KVM: X86: Don't reset mmu context when X86_CR4_PCIDE 1->0

X86_CR4_PCIDE doesn't participate in kvm_mmu_role, so the mmu context
doesn't need to be reset.  It is only required to flush all the guest
tlb.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210919024246.89230-2-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>