kconfig: add script to manipulate .config files on the command line

I often change single options in .config files. Instead of using
an editor or one of the frontends it's convenient to do this from
the command line. It's also useful to do from automated build scripts
when building different variants from a base config file.

I extracted most of the CONFIG manipulation code from one of my
build scripts into a new shell script scripts/config

The script is not integrated with the normal Kconfig machinery
and doesn't do any checking against Kconfig files, but just manipulates
that text format. This is always done at make time anyways.

I believe this script would be a useful standard addition for scripts/*

Sample usage:

./scripts/config --disable smp
Disable SMP in .config file

./scripts/config --file otherdir/.config --module e1000e
Enable E1000E as module in otherdir/.config

./scripts/config --state smp
y
Check state of config option CONFIG_SMP

After merging into git please make scripts/config executable

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>