stddef.h: move to generic code

stddef.h should be fairly generic across all platforms we'd want to
support, so let's move it to generic code.

Change-Id: I580c9c9b54f62fadd9ea97115933e16ea0b13ada
Signed-off-by: David Hendricks <dhendrix@chromium.org>
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: http://review.coreboot.org/2007
Tested-by: build bot (Jenkins)

src/include/stddef.h

@@ -0,0 +1,24 @@
+#ifndef STDDEF_H
+#define STDDEF_H
+
+typedef long ptrdiff_t;
+#ifndef __SIZE_TYPE__
+#define __SIZE_TYPE__ unsigned long
+#endif
+typedef __SIZE_TYPE__ size_t;
+typedef long ssize_t;
+
+typedef int wchar_t;
+typedef unsigned int wint_t;
+
+#define NULL ((void *)0)
+
+#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
+
+#ifdef __PRE_RAM__
+#define ROMSTAGE_CONST const
+#else
+#define ROMSTAGE_CONST
+#endif
+
+#endif /* STDDEF_H */