KVM: x86/mmu: Put refcounted pages instead of blindly releasing pfns

Now that all x86 page fault paths precisely track refcounted pages, use
Use kvm_page_fault.refcounted_page to put references to struct page memory
when finishing page faults.  This is a baby step towards eliminating
kvm_pfn_to_refcounted_page().

Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20241010182427.1434605-48-seanjc@google.com>