Hello,
The CPU_GetResetSource() method is not supported on Kinetis but you can use Cpu_OnReset(uint16_t Reason) event where the reset reason is provided as a parameter (value of RCM_SRS1 and RCM_SRS0 registers) or you can use PDD macros of RCM module, see below:
Best Regards,
Marek Neuzil