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/lib/tiny-printf.c b/lib/tiny-printf.c
index 0503c17..b8fc835 100644
--- a/lib/tiny-printf.c
+++ b/lib/tiny-printf.c
@@ -282,7 +282,7 @@
 					break;
 				}
 				islong = true;
-				/* no break */
+				fallthrough;
 			case 'x':
 				if (islong) {
 					num = va_arg(va, unsigned long);