Add support to disable specific ports, it's useful for some
scenarios:
1. usb3 PHY is shared whith PCIe or SATA, the corresponding
usb3 port can be disabled;
2. some usb2 or usb3 ports are not used on special platforms,
they should be disabled to save power.
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>