cfg: Fix Kinetis kwikstik/kx config

cfg: Fix Kinetis kwikstik/kx config

The flash definition belongs in the target cfg. Add some working area
and suitable reset_config.

Make kx.cfg more similar to klx.cfg.

Disable rclk as it is dead slow and a fixed 1MHz clock seems to work.

Change-Id: I8328f179c3a33be64403da93616abb48651bdfe6
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/2227
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-by: Paul Fertser <fercerpav@gmail.com>