ARM: at91: add atmel tcb capabilities

Some atmel socs have extra tcb capabilities that allow using a generic
clock source or enabling a quadrature decoder.

Signed-off-by: Kamel Bouhara <kamel.bouhara@bootlin.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>