phy: mediatek: tphy: add support force phy mode switch

phy: mediatek: tphy: add support force phy mode switch

this is used to be compatible with old SoCs, such as mt8195, which shares
t-phy between usb3 and pcie controller, usually, it's default mode is pcie
rc mode, and could use force mode to switch into usb3 mode, because pericfg
layer doesn't provide mode switch, also no efuse or jumper can be used;
Currently, only support switch from default pcie mode to usb3;
Note: don't use this way on new SoCs, use pericfg layer's mode switch
instead (by perperty "mediatek,syscon-type").

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/20231211025624.28991-2-chunfeng.yun@mediatek.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>