drivers: include standard header files from stpmic1_regulator.h

Add missing inclusion of stdbool.h and stddef.h in stpmic1_regulator.h.
The issue was revealed when upgrading to latest SCP-firmware source tree.

Fixes: 9cb0d51 ("drivers: stpmic1: export regulators API in a specific header file")
Signed-off-by: Etienne Carriere <etienne.carriere@foss.st.com>

core/include/drivers/stpmic1_regulator.h

@@ -1,11 +1,13 @@
 /* SPDX-License-Identifier: BSD-2-Clause */
 /*
- * Copyright (c) 2021-2022, STMicroelectronics
+ * Copyright (c) 2021-2024, STMicroelectronics
  */
 
 #ifndef __DRIVERS_STPMIC1_REGULATOR_H
 #define __DRIVERS_STPMIC1_REGULATOR_H
 
+#include <stdbool.h>
+#include <stddef.h>
 #include <stdint.h>
 
 /*