use proper fallthrough annotations

In some cases in the generic code, we were already using switch/case
fallthrough annotations comments, though in a way which might not be
understood by most compilers.

Replace two non-standard /* no break */ comments with our fallthrough;
statement-like macro, to make this visible to the compiler.
Also use this macro in place of an /* Fall through */ comment, to be
more consistent.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/common/command.c b/common/command.c
index 3f69139..0f9dd06 100644
--- a/common/command.c
+++ b/common/command.c
@@ -484,7 +484,7 @@
 		case 'q':
 			if (MEM_SUPPORT_64BIT_DATA)
 				return 8;
-			/* no break */
+			fallthrough;
 		default:
 			return CMD_DATA_SIZE_ERR;
 		}