soc/intel/baytrail/romstage/pmc.c: Add missing include

Replace unused <stddef.h> with missing <stdint.h>.

Change-Id: If8384f4fea66e26d7377311e7bd8379c7848a26f
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43345
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/baytrail/romstage/pmc.c

@@ -1,6 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
-#include <stddef.h>
+#include <stdint.h>
 #include <device/pci_ops.h>
 #include <console/console.h>
 #include <device/device.h>