The arch/$(ARCH)/defconfig is the hard-coded default in Kconfig,
and I want to deprecate it after evacuating the remaining defconfig
into the standard location, arch/*/configs/.
Define KBUILD_DEFCONFIG like other architectures, and move defconfig
into the configs/ subdirectory.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> Reviewed-by: Paul Walmsley <paul@pwsan.com>