hw: mcu: kinetis: remove custom systick
hw: mcu: kinetis: remove custom systick

Remove custom systick implementation and allow Kinetis MCUs to use the
existing `SysTick_Handler` implementation already available for
Cortex-M4 MCUs.

Signed-off-by: Fabio Utzig <66676b1ceaf93296e098708c09494361103aa635@apache.org>

mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core