kconfiglib: sync with the latest in Kconfiglib project

This commit imports some updates of kconfiglib.py from
https://github.com/ulfalizer/Kconfiglib



 - Warn about and ignore the "allnoconfig_y" Kconfig option
 - Statements in choices inherit menu/if deps
 - Add Symbol.is_allnoconfig_y()
 - Hint that modules are still supported despite warnings.
 - Add warning related to get_defconfig_filename().
 - Fix typo in docs.
 - Allow digits in $-references to symbols.

Signed-off-by: Ulf Magnusson <ulfalizer@gmail.com>
Signed-off-by: Philip Craig <philipjcraig@gmail.com>
Signed-off-by: Jakub Sitnicki <jsitnicki@gmail.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>