kbuild: redo fake deps at include/config/*.h

Make include/config/foo/bar.h fake deps files generation simpler.

* delete .h suffix
	those aren't header files, shorten filenames,

* delete tolower()
	Linux filesystems can deal with both upper and lowercase
	filenames very well,

* put everything in 1 directory
	Presumably 'mkdir -p' split is from dark times when filesystems
	handled huge directories badly, disks were round adding to
	seek times.

	x86_64 allmodconfig lists 12364 files in include/config.

	../obj/include/config/
	├── 104_QUAD_8
	├── 60XX_WDT
	├── 64BIT
		...
	├── ZSWAP_DEFAULT_ON
	├── ZSWAP_ZPOOL_DEFAULT
	└── ZSWAP_ZPOOL_DEFAULT_ZBUD

	0 directories, 12364 files

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
diff --git a/kernel/gen_kheaders.sh b/kernel/gen_kheaders.sh
index c1510f0..34a1dc2 100755
--- a/kernel/gen_kheaders.sh
+++ b/kernel/gen_kheaders.sh
@@ -36,7 +36,7 @@
 #
 # When Kconfig regenerates include/generated/autoconf.h, its timestamp is
 # updated, but the contents might be still the same. When any CONFIG option is
-# changed, Kconfig touches the corresponding timestamp file include/config/*.h.
+# changed, Kconfig touches the corresponding timestamp file include/config/*.
 # Hence, the md5sum detects the configuration change anyway. We do not need to
 # check include/generated/autoconf.h explicitly.
 #