feat(ff-a): feature retrieval through FFA_FEATURES call

Updated FFA_FEATURES according to FF-A v1.1 in SPMC can also be used
to retrieve feature information, and should now accept other arguments
than just FF-A call IDs.

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: I02cc24a31ab3092ec1ce6fed1a9649ffe7136782
1 file changed