dt-bindings: phy: mediatek: tphy: add a property for power-domains

dt-bindings: phy: mediatek: tphy: add a property for power-domains

Include the MediaTek TPHY in a power domain.  Add the 'power-domains'
property in the Device Tree (DT) Schema and set 'maxItems: 1'.

Also, include a reminder in the description of the 'power-domains'
property.

Signed-off-by: Macpaul Lin <macpaul.lin@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20241012035016.17667-1-macpaul.lin@mediatek.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>