usb: gadget: f_qdss: Add support for mdm qdss channel

Driver needs to pass qdss data received from mdm qdss
bridge driver to host PC. This requires a software data
path using IN endpoint. Bridge driver needs to open
qdss_mdm channel and use exported write() API to pass
the qdss data received from mdm. Driver calls the notify
call back upon write completion.

Change-Id: I4d8ceaed0bf9c85aa17d3f49503cd690917cc117
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>