[ARM] Fix SECURITY_INIT in linker script.

SECURITY_INIT doesn't work when it is placed inside an output section.
Use our own version instead.

arch/arm/vmlinux-armv.lds.in

@@ -53,7 +53,9 @@ SECTIONS
 		__con_initcall_start = .;
 			*(.con_initcall.init)
 		__con_initcall_end = .;
-		SECURITY_INIT
+		__security_initcall_start = .;
+			*(.security_initcall.init)
+		__security_initcall_end = .;
 		. = ALIGN(32);
 		__initramfs_start = .;
 			usr/built-in.o(.init.ramfs)