ARM: 9310/1: xip-kernel: add __inflate_kernel_data prototype

The kernel .data decompression is called from assembler, so it does
not need a prototype, but adding one avoids this W=1 warning:

arch/arm/kernel/head-inflate-data.c:35:12: error: no previous prototype for '__inflate_kernel_data' [-Werror=missing-prototypes]

The same file contains a few extern declarations for assembler
symbols, move those into the header as well for consistency.

Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

arch/arm/kernel/head-inflate-data.c

@@ -8,16 +8,13 @@
 
 #include <linux/init.h>
 #include <linux/zutil.h>
+#include "head.h"
 
 /* for struct inflate_state */
 #include "../../../lib/zlib_inflate/inftrees.h"
 #include "../../../lib/zlib_inflate/inflate.h"
 #include "../../../lib/zlib_inflate/infutil.h"
 
-extern char __data_loc[];
-extern char _edata_loc[];
-extern char _sdata[];
-
 /*
  * This code is called very early during the boot process to decompress
  * the .data segment stored compressed in ROM. Therefore none of the global

arch/arm/kernel/head.h

@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+extern char __data_loc[];
+extern char _edata_loc[];
+extern char _sdata[];
+
+int __init __inflate_kernel_data(void);