usb: misc: Add support for diag bridging over mdm_data_bridge

Add support for bridging diag messages over mdm_data_bridge
instead of the traditional diag_bridge and char drivers. This
simplifies the design and helps with better handling of diag EP
polling in throughput intensive cases on telematics platforms.

Change-Id: I6e6f3259cb6371796d9b6a9f2d824dca5576ed4a
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>