feat(notifications): add RX buffer full notification helper functions

Add RX buffer full framework notification defines and helper
functions.
RX buffer full notification is set by the partition manager (either
hypervisor or SPMC) when delivering a message using FF-A v1.1
FFA_MSG_SEND2 indirect message ABI.

Change-Id: I6ab01c1ca4090d2686ce747f14da76b5307b8332
Signed-off-by: Federico Recanati <federico.recanati@arm.com>
diff --git a/src/vm.c b/src/vm.c
index f67bdd6..2c479f3 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -716,7 +716,8 @@
 	struct vm_locked vm_locked, ffa_notifications_bitmap_t notifications)
 {
 	CHECK(vm_locked.vm != NULL);
-	assert(notifications == 0x1U);
+	assert(is_ffa_spm_buffer_full_notification(notifications) ||
+	       is_ffa_hyp_buffer_full_notification(notifications));
 	vm_notifications_state_set(&vm_locked.vm->notifications.framework,
 				   notifications);
 }