phy: rockchip-typec: force to USB2 if DP at 4 lanes mode

The usb3tousb2_en BIT will be clear to 0 in probe(), it make USB
controller work at USB3 mode, and if the USB phy is turned on with DP
only mode(4 lanes DP), the rockchip_usb3_phy_power_on() will return
directly, so usb3_host_disable and usb3_host_port these 2 BIT will keep
a same value as coreboot. In coreboot, these 3 BITs are set as USB2
mode, but now one of the bits is changed to USB3, it make USB controller
work at a unknown status.

These 3 BITs should be changed to USB2, if the Type-C works at 4 lanes
mode, and then switch it back to USB3 mode, when USB disconnect.

Signed-off-by: Chris Zhong <zyw@rock-chips.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>