dwc_otg: Provide sysfs interface to user space to switch host mode and

dwc_otg: Provide sysfs interface to user space to switch host mode and
device mode.

BZ: 29834

Because currently there is no workable micro A usb3 cable on market. So
provide sysfs interface to support switch host mode and device mode from
user space.

Usage(commands):
switch to host: echo A > /sys/devices/pci0000:00/0000:00:11:0/otg_id
switch to device: echo A > /sys/devices/pci0000:00/0000:00:11:0/otg_id

Signed-off-by: Yu Wang <yu.y.wang@intel.com>
Change-Id: I60a4cefa72508f6f3dc70abbea5bc8f954eb644b
Signed-off-by: Yu Wang <yu.y.wang@intel.com>
Reviewed-on: http://android.intel.com:8080/41865
Reviewed-by: Meng, Zhe <zhe.meng@intel.com>
Tested-by: Meng, Zhe <zhe.meng@intel.com>
Reviewed-by: Tang, Richard <richard.tang@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>