usb: ucsi: huawei_gaokun: support mode switching

The USB PHY (QMP Combo PHY) is always initialized in USB3+DP mode. In
the past, there was no MUX, and it was unnecessary to set it, since
MSM only supported 2-lane DP. But now, MST and 4-lane DP support has
been added to MSM, and a MUX has been added to the PHY. To support
4-lane DP and mode switching for gaokun, get the MUX and set it.

Signed-off-by: Pengyu Luo <mitltlatltl@gmail.com>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://patch.msgid.link/20260607101844.820064-1-mitltlatltl@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>