dt-bindings: microchip: atmel,at91rm9200-tcb: add sama5d2 compatible

The sama5d2 TC block TIMER_CLOCK1 is different from the at91sam9x5 one.
Instead of being MCK / 2, it is the TCB GCLK.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20200710230813.1005150-3-alexandre.belloni@bootlin.com