Hi Matthieu,
Please find your Kinetis device Reference Manual. Example: http://cache.freescale.com/files/microcontrollers/doc/ref_manual/K64P144M120SF5RM.pdf?fasp=1&WT_TYPE...
The Signal Multiplexing and Signal Description chapter will should how each pin is configured by Default.
In general GPIO pins are disabled so High Impedance. Analog pins are enabled.
Regards,
David