mediatek: filogic: set correct PWM clock and clean thermal zone

mediatek: filogic: set correct PWM clock and clean thermal zone

 * set correct clocks for PWM to work.
 * MT7986 PWM does have the 26MHz-clock-select, set that in patch
 * drop useless 'passive' trip point in thermal zone
 * extend pwm-fan to have 3 active operating points
 * set reasonable trip points in thermal zone
 * invert pwm-fan operating points and set shorter period to allow
   less noisy operation of the PWM fan of the BPi-R3.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>