linux/time.h: Extract common header for vDSO

The vDSO library should only include the necessary headers required for
a userspace library (UAPI and a minimal set of kernel headers). To make
this possible it is necessary to isolate from the kernel headers the
common parts that are strictly necessary to build the library.

Split time.h into linux and common headers to make the latter suitable
for inclusion in the vDSO library.

Signed-off-by: Vincenzo Frascino <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

include/linux/time.h

···
  */
 #define time_between32(t, l, h) ((u32)(h) - (u32)(l) >= (u32)(t) - (u32)(l))
 
-struct timens_offset {
-	s64	sec;
-	u64	nsec;
-};
+# include <vdso/time.h>
 
 #endif

include/vdso/time.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __VDSO_TIME_H
+#define __VDSO_TIME_H
+
+#include <uapi/linux/types.h>
+
+struct timens_offset {
+	s64	sec;
+	u64	nsec;
+};
+
+#endif /* __VDSO_TIME_H */