arm64: vdso: Use generic union vdso_data_store

There is already a generic union definition for vdso_data_store in vdso
datapage header.

Use this definition to prevent code duplication.
Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20240219153939.75719-6-anna-maria@linutronix.de

arch/arm64/kernel/vdso.c

@@ -69,10 +69,7 @@ static struct vdso_abi_info vdso_info[] __ro_after_init = {
 /*
  * The vDSO data page.
  */
-static union {
-	struct vdso_data	data[CS_BASES];
-	u8			page[PAGE_SIZE];
-} vdso_data_store __page_aligned_data;
+static union vdso_data_store vdso_data_store __page_aligned_data;
 struct vdso_data *vdso_data = vdso_data_store.data;
 
 static int vdso_mremap(const struct vm_special_mapping *sm,