kconfig: use distinct tokens for type and default properties

This commit removes kconf_id::stype to prepare for the entire
removal of kconf_id.c

To simplify the lexer, I want keywords straight-mapped to tokens.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>