drivers: pwm: mcux: ftm: fix pwm capture timer overflow count edge cases

Depending on the timing of the edges of the signal to be captured, a timer
overflow interrupt flag may appear in the same ISR as a channel event (1st
or 2nd edge capture complete) flag. Change the timer overflow math to
compensate the timer overflow count based on whether the channel event
happened before or after the overflow flag occured.

For continuous PWM period captures, only the very first edge of the first
period requires an interrupt to be captured. Subsequent "first edges" are
the same edges as the second edge of the previous period. Depending on the
timing of the captured signal, enabling the 1st edge interrupt in this case
can cause the overflow count for subsequent first edges to be captured at
the wrong point in time.

Fixes: #52452

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>
(cherry picked from commit b4912ea9)