kbuild: generate modules.order only in directories visited by obj-y/m

[ Upstream commit 4f2c8f3089f538f556c86f26603a062865e4aa94 ]

The modules.order files in directories visited by the chain of obj-y
or obj-m are merged to the upper-level ones, and become parts of the
top-level modules.order. On the other hand, there is no need to
generate modules.order in directories visited by subdir-y or subdir-m
since they would become orphan anyway.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Stable-dep-of: 2e3d0e20d845 ("ARM: dts: exynos: correct TMU phandle in Odroid HC1")
Signed-off-by: Sasha Levin <sashal@kernel.org>