KVM: x86/mmu: Replace open coded usage of tdp_mmu_page with is_tdp_mmu_page()

KVM: x86/mmu: Replace open coded usage of tdp_mmu_page with is_tdp_mmu_page()

[ Upstream commit aeb568a1a6041e3d69def54046747bbd989bc4ed ]

Use is_tdp_mmu_page() instead of querying sp->tdp_mmu_page directly so
that all users benefit if KVM ever finds a way to optimize the logic.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221012181702.3663607-10-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Stable-dep-of: edbdb43fc96b ("KVM: x86: Preserve TDP MMU roots until they are explicitly invalidated")
Signed-off-by: Sasha Levin <sashal@kernel.org>