dt-bindings: phy: mediatek: tphy: add a property for force-mode switch

dt-bindings: phy: mediatek: tphy: add a property for force-mode switch

Due to some old SoCs with shared t-phy between usb3 and pcie only support
force-mode switch, and shared and non-shared t-phy may exist at the same
time on a SoC, can't use compatible to distinguish between shared and
non-shared t-phy, add a property to supported it.
Currently, only support switch from default pcie mode to usb3 mode.
But now prefer to use "mediatek,syscon-type" on new SoC as far as possible.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231211025624.28991-1-chunfeng.yun@mediatek.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>