checkpatch: kconfig: check help texts for menuconfig and choice

Currently, only Kconfig symbols are checked for a missing or short help
text, and are only checked if they are defined with the 'config'
keyword.

To make the check more general, extend it to also check help texts for
choices and for symbols defined with the 'menuconfig' keyword.

This increases the accuracy of the check for symbols that would already
have been checked as well, since e.g. a 'menuconfig' symbol after a help
text will be recognized as ending the preceding symbol/choice
definition.

To increase the accuracy of the check further, also recognize 'if',
'endif', 'menu', 'endmenu', 'endchoice', and 'source' as ending a
symbol/choice definition.

Signed-off-by: Ulf Magnusson <ulfalizer@gmail.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>