dt-bindings: timer: Add support for cadence TTC PWM

Cadence TTC can act as PWM device, it will be supported through
separate PWM framework based driver. Decision to configure
specific TTC device as PWM or clocksource/clockevent would
be done based on presence of "#pwm-cells" property.

Also, interrupt property is not required for TTC PWM driver.
Update bindings to support TTC PWM configuration.

Signed-off-by: Mubin Sayyed <mubin.sayyed@amd.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20240226093333.2581092-1-mubin.sayyed@amd.com