Kinetis: suppress false alarms "MCU is secured"

Kinetis driver checks MDM STAT register to detect secured state of MCU.
An unsecured clean device typically triggered a huge fat alarm message.
Now when driver detects secured state it tries to halt MCU and then
re-reads status register.

Command "mdm mass_erase" used to deassert reset when finished
and MCU started looping in hard fault - WDOG reset cycle.
Now "reset halt" is issued. Clean flash is not run after mass_erase.

Change-Id: I23f393509fbd8751d44ffc744ff2d67f1074f74e
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/3010


Tested-by: jenkins
Reviewed-by: Thomas Schmid <thomas@rfranging.com>
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>