KVM: x86/mmu: Fold mmu_spte_update_no_track() into mmu_spte_update()

Fold the guts of mmu_spte_update_no_track() into mmu_spte_update() now
that the latter doesn't flush when clearing A/D bits, i.e. now that there
is no need to explicitly avoid TLB flushes when aging SPTEs.

Opportunistically WARN if mmu_spte_update() requests a TLB flush when
aging SPTEs, as aging should never modify a SPTE in such a way that KVM
thinks a TLB flush is needed.

Link: https://lore.kernel.org/r/20241011021051.1557902-8-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>