usb: langwell_udc: use common OTG data structure for Intel MID platform

usb: langwell_udc: use common OTG data structure for Intel MID platform

This patch provided the support to common OTG data structure.

Main changes:
- Notify otg related events using notifier and remove direct
  access to otg data structure(state machine).
- Provide start_peripheral/stop_peripheral function to transceiver.
- Provide client register/unregister function.

  modified:   drivers/usb/gadget/langwell_udc.c
  modified:   drivers/usb/gadget/langwell_udc.h

Change-Id: Icfa1f5171a2459fe7d9098c842777b488bf48aaa
Signed-off-by: Hao Wu <hao.wu@intel.com>
Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>