x86/vdso: Access vdso data without vvar.h

The vdso_data is at the start of the vvar page.
Make use of this invariant to remove the usage of vvar.h.
This also matches the logic for the timens data.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20241010-vdso-generic-base-v1-18-b64f0842d512@linutronix.de

Author: t-8ch

arch/x86/entry/vdso/vdso-layout.lds.S

@@ -20,11 +20,6 @@ SECTIONS
 	vvar_start = . - 4 * PAGE_SIZE;
 	vvar_page  = vvar_start;
 
-	/* Place all vvars at the offsets in asm/vvar.h. */
-#define EMIT_VVAR(name, offset) vvar_ ## name = vvar_page + offset;
-#include <asm/vvar.h>
-#undef EMIT_VVAR
-
 	vdso_rng_data = vvar_page + __VDSO_RND_DATA_OFFSET;
 
 	pvclock_page = vvar_start + PAGE_SIZE;

arch/x86/include/asm/vdso/gettimeofday.h

@@ -14,13 +14,13 @@
 
 #include <uapi/linux/time.h>
 #include <asm/vgtod.h>
-#include <asm/vvar.h>
 #include <asm/unistd.h>
 #include <asm/msr.h>
 #include <asm/pvclock.h>
 #include <clocksource/hyperv_timer.h>
 
-#define __vdso_data (VVAR(_vdso_data))
+extern struct vdso_data vvar_page
+	__attribute__((visibility("hidden")));
 
 extern struct vdso_data timens_page
 	__attribute__((visibility("hidden")));
@@ -277,7 +277,7 @@ static inline u64 __arch_get_hw_counter(s32 clock_mode,
 
 static __always_inline const struct vdso_data *__arch_get_vdso_data(void)
 {
-	return __vdso_data;
+	return &vvar_page;
 }
 
 static inline bool arch_vdso_clocksource_ok(const struct vdso_data *vd)