src/ec: Use 'include <stdlib.h>' when appropriate

Change-Id: Ifdb2dee08da45d698174583ee5ed44bf5a0243ff
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32823
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>

src/ec/quanta/ene_kb3940q/ec.c

@@ -22,7 +22,6 @@
 #include <device/pnp.h>
 #include <delay.h>
 #include <elog.h>
-#include <stdlib.h>
 #include <pc80/keyboard.h>
 
 #include "ec.h"

src/ec/quanta/it8518/ec.c

@@ -20,7 +20,6 @@
 #include <device/device.h>
 #include <device/pnp.h>
 #include <pc80/keyboard.h>
-#include <stdlib.h>
 
 #include "ec.h"
 #include "chip.h"