ANDROID: KVM: arm64: Advertise support for FFA_RX_RELEASE

The guest FFA handler supports FFA_RX_RELEASE but do_ffa_guest_features
reports that it is unsupported. This can prevent guests from discovering
and using this API to return a transferred buffer to its original owner.
Enable support by adding FFA_RX_RELEASE case to the feature discovery
switch statement.

Bug: 269285339
Bug: 278749606
Change-Id: Iecaefedd51614cb81b82303e68fa8a759e579e50
Signed-off-by: Per Larsen <perlarsen@google.com>