Switch to the new pwm-atmel-tcb binding that avoid wasting TCB channels.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Antoine Aubert <a.aubert@overkiz.com>
Link: https://lore.kernel.org/r/20201030183658.1007395-5-alexandre.belloni@bootlin.com