DM USB: xHCI: modify option parsing function to enable USB virtualiztion

Re-write the xHCI option parse function to support port mapper.

The new usage:
  -s <n>,xhci,[bus1-port1,bus2-port2]:[tablet]
  eg: -s 8,xhci,1-2,2-2
  eg: -s 7,xhci,tablet
  eg: -s 7,xhci,1-2,2-2:tablet

Note: please follow the board hardware design, assign the ports
according to the receptacle connection

Change-Id: I3c8392f7e15580cf768c8c4a619d705411da699d
Signed-off-by: Wu, Xiaoguang <xiaoguang.wu@intel.com>
Reviewed-by: Shuo Liu <shuo.a.liu@intel.com>
Reviewed-by: Yu Wang <yu1.wang@intel.com>
Reviewed-by: Zhao Yakui <yakui.zhao@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

Author: xiaoguangwu