refactor: rename type for FF-A IDs

The FF-A ID is a unsigned 16-bit value that was named
ffa_vm_id_t. This patch changes it to simply ffa_id_t.
This is to make clearer the ID type is used for other
endpoints other than simply VMs.

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: I60319c08481b2380bd0063b108a35fc01e2af537
diff --git a/src/dlog.c b/src/dlog.c
index ca46bb6..784c1f6 100644
--- a/src/dlog.c
+++ b/src/dlog.c
@@ -221,7 +221,7 @@
  * Send the contents of the given VM's log buffer to the log, preceded by the VM
  * ID and followed by a newline.
  */
-void dlog_flush_vm_buffer(ffa_vm_id_t id, char buffer[], size_t length)
+void dlog_flush_vm_buffer(ffa_id_t id, char buffer[], size_t length)
 {
 	lock();