arm64: vdso: add __init section marker to alloc_vectors_page

It is not needed after booting, this patch moves the alloc_vectors_page
function to the __init section.
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/vdso.c

@@ -55,7 +55,7 @@ struct vdso_data *vdso_data = &vdso_data_store.data;
  */
 static struct page *vectors_page[1];
 
-static int alloc_vectors_page(void)
+static int __init alloc_vectors_page(void)
 {
 	extern char __kuser_helper_start[], __kuser_helper_end[];
 	extern char __aarch32_sigret_code_start[], __aarch32_sigret_code_end[];