feat(ffa-svc): add `ffa_func_name` and `ffa_error_name`

Adds helper functions for getting string representations of function
identifiers and error codes. This makes debug logs more readable than
printing the integer value.

Change-Id: I9e74c197686dc08e0c71886f641c60829587bad6
Signed-off-by: Karl Meakin <karl.meakin@arm.com>
diff --git a/spm/ivy/app/ivy_main.c b/spm/ivy/app/ivy_main.c
index 1e2cd6a..861ef30 100644
--- a/spm/ivy/app/ivy_main.c
+++ b/spm/ivy/app/ivy_main.c
@@ -42,8 +42,8 @@
 	VERBOSE("Mapping RXTX Regions\n");
 	CONFIGURE_AND_MAP_MAILBOX(mb, PAGE_SIZE, ret);
 	if (ffa_func_id(ret) != FFA_SUCCESS_SMC32) {
-		ERROR("Failed to map RXTX buffers. Error %x\n",
-		      ffa_error_code(ret));
+		ERROR("Failed to map RXTX buffers. Error %s\n",
+		      ffa_error_name(ffa_error_code(ret)));
 		panic();
 	}
 
@@ -53,7 +53,8 @@
 
 	while (1) {
 		if (ffa_func_id(ret) != FFA_MSG_SEND_DIRECT_REQ_SMC32) {
-			ERROR("unknown FF-A request %x\n", ffa_func_id(ret));
+			ERROR("unknown FF-A request %s\n",
+			      ffa_func_name(ffa_func_id(ret)));
 			goto init;
 		}