dt-bindings: watchdog: Add SMARC-sAM67 support

The SMARC-sAM67 board has an on-board uC which has the same register
interface as the older CPLD implementation on the SMARC-sAL28 board.
Although the MCU emulates the same behavior, be prepared for any quirks
and add a board specific compatible.

Signed-off-by: Michael Walle <mwalle@kernel.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Lee Jones <lee@kernel.org>