kvm: mmu: Use fast PF path for access tracking of huge pages when possible

The fast page fault path bails out on write faults to huge pages in
order to accommodate dirty logging. This change adds a check to do that
only when dirty logging is actually enabled, so that access tracking for
huge pages can still use the fast path for write faults in the common
case.

Signed-off-by: Junaid Shahid <junaids@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211104003359.2201967-1-junaids@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>