arch: st_stm32: Include errno.h

The files soc_config.c and soc_gpio.c use errno code so they should
include errno.h.

Change-Id: I94237aa294701cc71ed17ea42eca9d8073d4ae47
Signed-off-by: Andre Guedes <andre.guedes@intel.com>

arch/arm/soc/st_stm32/stm32f1/soc_config.c

@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+#include <errno.h>
+
 #include "soc.h"
 #include <device.h>
 #include <misc/util.h>

arch/arm/soc/st_stm32/stm32f1/soc_gpio.c

@@ -25,6 +25,8 @@
  *            (GPIOs and AFIOs)
  */
 
+#include <errno.h>
+
 #include <device.h>
 #include "soc.h"
 #include "soc_registers.h"