kconfig: fork mconf source from olibc

Added from commit 424a2e4 of https://github.com/olibc/kconfig
with the following commit reverted

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commit e9eb3dd3b239ea10ed34cc8566ebb5bb5b37f8d0
Author: Kito Cheng <kito@0xlab.org>
Date:   Tue Jun 11 22:56:50 2013 +0800

    Output boolean value '=true' instead of '=y'
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kconfig: fix naming from olibc to F9 microkernel
mk: add kconfig support

new make target:
  1. config: parse Kconfig and introduce config menu
  2. distclean: clean project, then clean config files