KVM: arm64: Use __gfn_to_page() when copying MTE tags to/from userspace

Use __gfn_to_page() instead when copying MTE tags between guest and
userspace.  This will eventually allow removing gfn_to_pfn_prot(),
gfn_to_pfn(), kvm_pfn_to_refcounted_page(), and related APIs.

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: <20241010182427.1434605-78-seanjc@google.com>