commonlib/bsd, libpayload: Do not include helpers.h in stddef.h

`stddef.h` should only provide the definitions defined by ISO or Posix.
The included `commonlib/bsd/helpers.h` provide a lot of non standard
definitions that may interfere with definitions from the application.

Change-Id: Ia71edbc3ffe6694ff4b971decf3a41f915264bc8
Signed-off-by: Thomas Heijligen <src@posteo.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/70116
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

payloads/libpayload/arch/x86/boot_media.c

@@ -1,11 +1,7 @@
 /* SPDX-License-Identifier: BSD-3-Clause */
 
-#include <arch/virtual.h>
+#include <libpayload.h>
 #include <boot_device.h>
-#include <commonlib/bsd/cb_err.h>
-#include <stddef.h>
-#include <string.h>
-#include <sysinfo.h>
 
 __attribute__((weak)) ssize_t boot_device_read(void *buf, size_t offset, size_t size)
 {