If CONFIG_USE_BUILTIN_DTB is enabled, but CONFIG_BUILTIN_DTB_SOURCE
is empty (for example, allmodconfig), it fails to build, like this:
make[2]: *** No rule to make target 'arch/sh/boot/dts/.dtb.o',
needed by 'arch/sh/boot/dts/built-in.o'. Stop.
Surround obj-y with ifneq ... endif.
I replaced $(CONFIG_USE_BUILTIN_DTB) with 'y' since this is always
the case from the following code from arch/sh/Makefile:
core-$(CONFIG_USE_BUILTIN_DTB) += arch/sh/boot/dts/
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>