libpayload/sys/types.h: Add definition for off_t

`off_t` is supposed to be signed, but has no (minimum) width
specified. We'll assume 32-bit minimum, like a `signed long int`.

Also include `sys/types.h` in `libpayload.h` so everything is
available through the latter.

Change-Id: I6c0c1bc1a959db7863cbad2ba29318da162431be
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/c/31346
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

payloads/libpayload/include/libpayload.h

@@ -58,6 +58,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
+#include <sys/types.h>
 #include <arch/types.h>
 #include <arch/io.h>
 #include <arch/virtual.h>

payloads/libpayload/include/sys/types.h

@@ -27,4 +27,11 @@
  * SUCH DAMAGE.
  */
 
+#ifndef _SYS_TYPES_H
+#define _SYS_TYPES_H
+
 #include <arch/types.h>
+
+typedef signed long int off_t;
+
+#endif /* _SYS_TYPES_H */