ARM_ATAG_DTB_COMPAT fails on fdt_ro.c compiling

[Shawn Guo]

I have seen this error on mainline for a couple days when
ARM_ATAG_DTB_COMPAT is enabled.

  CC      arch/arm/boot/compressed/fdt_ro.o
arch/arm/boot/compressed/fdt_ro.c: In function ‘fdt_path_offset’:
arch/arm/boot/compressed/fdt_ro.c:172:3: error: implicit declaration of function ‘fdt_get_alias_namelen’ [-Werror=implicit-function-declaration]
arch/arm/boot/compressed/fdt_ro.c:172:5: warning: assignment makes pointer from integer without a cast [enabled by default]
arch/arm/boot/compressed/fdt_ro.c: At top level:
arch/arm/boot/compressed/fdt_ro.c:340:13: error: conflicting types for ‘fdt_get_alias_namelen’
arch/arm/boot/compressed/fdt_ro.c:172:7: note: previous implicit declaration of ‘fdt_get_alias_namelen’ was here
cc1: some warnings being treated as errors

Shawn