kbuild: use more subdir- for visiting subdirectories while cleaning

Documentation/kbuild/makefiles.rst suggests to use "archclean" for
cleaning arch/$(SRCARCH)/boot/, but it is not a hard requirement.

Since commit d92cc4d51643 ("kbuild: require all architectures to have
arch/$(SRCARCH)/Kbuild"), we can use the "subdir- += boot" trick for
all architectures. This can take advantage of the parallel option (-j)
for "make clean".

I also cleaned up the comments in arch/$(SRCARCH)/Makefile. The "archdep"
target no longer exists.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/arc/Kbuild b/arch/arc/Kbuild
index 699d8cae9b1f..b94102fff68b 100644
--- a/arch/arc/Kbuild
+++ b/arch/arc/Kbuild
@@ -1,3 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-y += kernel/
 obj-y += mm/
+
+# for cleaning
+subdir- += boot