Use stopwatch_wait_until_expired where applicable

Change-Id: I4d6c6810b91294a7e401a4a1a446218c04c98e55
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-on: https://review.coreboot.org/21590
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Mario Scheithauer <mario.scheithauer@siemens.com>

src/lib/timer.c

@@ -34,7 +34,5 @@ void udelay(unsigned int usec)
 		return;
 
 	stopwatch_init_usecs_expire(&sw, usec);
-
-	while (!stopwatch_expired(&sw))
-		;
+	stopwatch_wait_until_expired(&sw);
 }