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/inc/hf/arch/ffa.h b/inc/hf/arch/ffa.h
index d36a4be..ca17b99 100644
--- a/inc/hf/arch/ffa.h
+++ b/inc/hf/arch/ffa.h
@@ -14,7 +14,7 @@
 struct ffa_value arch_ffa_features(uint32_t function_id);
 
 /** Returns the SPMC ID. */
-ffa_vm_id_t arch_ffa_spmc_id_get(void);
+ffa_id_t arch_ffa_spmc_id_get(void);
 
 /** Called once at boot time to initialize the platform ffa module. */
 void arch_ffa_init(void);