KVM: PPC: Use __kvm_faultin_pfn() to handle page faults on Book3s Radix

KVM: PPC: Use __kvm_faultin_pfn() to handle page faults on Book3s Radix

Replace Book3s Radix's homebrewed (read: copy+pasted) fault-in logic with
__kvm_faultin_pfn(), which functionally does pretty much the exact same
thing.

Note, when the code was written, KVM indeed didn't do fast GUP without
"!atomic && !async", but that has long since changed (KVM tries fast GUP
for all writable mappings).

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: <20241010182427.1434605-62-seanjc@google.com>