fix(ff-a): default print verbosity

Changed to verbose print:
INFO:   Memory region 0x71fc000 - 0x7200000 allocated

SMMU id unspecified for a given peripheral:
WARNING: SMMUv3: Unexpected smmu-id:4294967295 specified in manifest

'FF-A RXTX Unmap API consecutive' test:
ERROR: No buffer pair registered on behalf of the caller.

Change-Id: Ibc20d7e7e0ab51f4343fbdf0914cf4aa2b8e71d4
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
diff --git a/src/api.c b/src/api.c
index e5b7bb6..542b461 100644
--- a/src/api.c
+++ b/src/api.c
@@ -1152,7 +1152,7 @@
 
 	/* Get send and receive buffers. */
 	if (vm->mailbox.send == NULL || vm->mailbox.recv == NULL) {
-		dlog_error(
+		dlog_verbose(
 			"No buffer pair registered on behalf of the caller.\n");
 		return ffa_error(FFA_INVALID_PARAMETERS);
 	}