drviers: pwm: Update flexio pwm update duty cycle

Updated the nxp flexio pwm driver to account
for when the duty cycle is 100% or 0%.
We switch off the counter of the flexio and
manually set the GPIO High or Low. Otherwise
Flexio Peripheral with default to a 50% duty
cycle behavior.
Factored out timerOutput variable.

Signed-off-by: Emilio Benavente <emilio.benavente@nxp.com>