MIPS: boot: Fix unaligned access with CONFIG_MIPS_RAW_APPENDED_DTB

The compressed payload is not necesarily 4-byte aligned, at least when
compiling with Clang. In that case, the 4-byte value appended to the
compressed payload that corresponds to the uncompressed kernel image
size must be read using get_unaligned_le32().

This fixes Clang-built kernels not booting on MIPS (tested on a Ingenic
JZ4770 board).

Fixes: b8f54f2c ("MIPS: ZBOOT: copy appended dtb to the end of the kernel")
Cc: <stable@vger.kernel.org> # v4.7
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/boot/compressed/decompress.c

@@ -13,6 +13,7 @@
 #include <linux/libfdt.h>
 
 #include <asm/addrspace.h>
+#include <asm/unaligned.h>
 
 /*
  * These two variables specify the free mem region
@@ -117,7 +118,7 @@ void decompress_kernel(unsigned long boot_heap_start)
 		dtb_size = fdt_totalsize((void *)&__appended_dtb);
 
 		/* last four bytes is always image size in little endian */
-		image_size = le32_to_cpup((void *)&__image_end - 4);
+		image_size = get_unaligned_le32((void *)&__image_end - 4);
 
 		/* copy dtb to where the booted kernel will expect it */
 		memcpy((void *)VMLINUX_LOAD_ADDRESS_ULL + image_size,