vdso: Introduce vdso/page.h

vdso: Introduce vdso/page.h

The VDSO implementation includes headers from outside of the
vdso/ namespace.

Introduce vdso/page.h to make sure that the generic library
uses only the allowed namespace.

Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> # m68k
Link: https://lore.kernel.org/all/20241014151340.1639555-3-vincenzo.frascino@arm.com