kinetis-tpm: Implement pulse_cycles directly instead of duty cycle

When using low PWM frequency i.e 50Hz the resolution of pulse_cycles
got lost from converting pulse_cycles to duty cycle % and then back to
pulse_cycles again.

Furthermore TPM_UpdateChnlEdgeLevelSelect call would restart the pwm
constantly on a mcux_tpm_set_cycles call now only call
TPM_UpdateChnlEdgeLevelSelect when changing the polarity

Signed-off-by: Peter van der Perk <peter.vanderperk@nxp.com>