KVM: x86/xen: advertize the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA capability

Now that all relevant kernel changes and selftests are in place, enable the
new capability.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20240215152916.1158-17-paul@xen.org


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