kconfig: Add scripts/Kconfig.include from v4.19

kconfig: Add scripts/Kconfig.include from v4.19

As part of re-syncing our Kconfig logic up to v4.19, we had missed
adding this new file that includes helper macros.  To quote the upstream
commit e1cfdc0e72fc ("kconfig: add basic helper macros to scripts/Kconfig.include"):

Kconfig got text processing tools like we see in Make.  Add Kconfig
helper macros to scripts/Kconfig.include like we collect Makefile
macros in scripts/Kbuild.include.

Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Tom Rini <trini@konsulko.com>