src: include <assert.h> when appropriate

Change-Id: Ib843eb7144b7dc2932931b9e8f3f1d816bcc1e1a
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/26796
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: David Guckian

src/soc/intel/skylake/gpio.c

@@ -14,7 +14,6 @@
  * GNU General Public License for more details.
  */
 
-#include <assert.h>
 #include <intelblocks/gpio.h>
 #include <intelblocks/pcr.h>
 #include <soc/pcr_ids.h>