BACKPORT: arm: Introduce asm/vdso/clocksource.h

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.

Introduce asm/vdso/clocksource.h to contain all the arm64 specific
functions that are suitable for vDSO inclusion.

This header will be required by a future patch that will generalize
vdso/clocksource.h.

Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Russell King <linux@armlinux.org.uk>
Link: https://lkml.kernel.org/r/20200320145351.32292-6-vincenzo.frascino@arm.com
(cherry picked from commit c16b270b17)
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 154668398
Change-Id: I0f3f58c95e64fbb706f49dc66e28562ca95f22d3

arch/arm/include/asm/clocksource.h

@@ -1,8 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 #ifndef _ASM_CLOCKSOURCE_H
 #define _ASM_CLOCKSOURCE_H
 
-struct arch_clocksource_data {
-	bool vdso_direct;	/* Usable for direct VDSO access? */
-};
+#include <asm/vdso/clocksource.h>
 
-#endif
+#endif /* _ASM_CLOCKSOURCE_H */

arch/arm/include/asm/vdso/clocksource.h

@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_VDSOCLOCKSOURCE_H
+#define __ASM_VDSOCLOCKSOURCE_H
+
+struct arch_clocksource_data {
+	bool vdso_direct;	/* Usable for direct VDSO access? */
+};
+
+#endif /* __ASM_VDSOCLOCKSOURCE_H */