xtensa: annotate dtb_start variable as static __initdata

The 'dtb_start' variable is only used within arch/xtensa/kernel/setup.c.
Mark it as 'static'.

It is only used by parse_tag_fdt() and init_arch(), both of which are
annotated as __init. Therefore, dtb_start can be annotated as __initdata,
so it will discarded after boot.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Message-Id: <20240918031537.588965-1-masahiroy@kernel.org>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

Author: masahir0y

arch/xtensa/kernel/setup.c

@@ -55,7 +55,7 @@ extern int initrd_below_start_ok;
 #endif
 
 #ifdef CONFIG_USE_OF
-void *dtb_start = __dtb_start;
+static void *dtb_start __initdata = __dtb_start;
 #endif
 
 extern unsigned long loops_per_jiffy;