kconfig: update to Linux 5.2-rc4 ...

The previous sync was Linux 4.20. This updates Kconfig to Linux 5.2-rc4.

I adjusted the top Makefile as well because Linux commit 058507195b53
("kbuild: move ".config not found!" message from Kconfig to Makefile")
moved the .config check from Kconfig to Makefile.

I also made auto.conf a mandatory include file, and remove it from the
prerequisites of other targets. We are safe because Make is immediately
terminated when syncconfig fails to generate auto.conf.

Highlights:

 - The parser has no more shift/reduce conflicts

 - The lexer was rewritten more simply

 - The token lookup table was deleted

 - Replace license boilerplates with SPDX

 - Compile C files as separate units

 - Do not overwrite .config when the content was not changed

 - Lots of bug-fixes and cleanups

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>