dt-bindings: counter: microchip-tcb-capture counter

Describe the devicetree binding for the Microchip TCB module.
Each counter blocks exposes three independent counters.

However, when configured in quadrature decoder, both channel <0> and <1>
are required for speed/position and rotation capture (yet only the
position is captured).

Signed-off-by: Kamel Bouhara <kamel.bouhara@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>