USB: gadget: add BAM-DMUX transport for DPL function

A new logical BAM-DMUX channel is created for routing the DPL traffic.
Add BAM-DMUX transport support for the QDSS function driver that is
used for the DPL function. The QTI control transport is already
in place for the DPL function. Update the BAM-DMUX logical channel
assigned for DPL so that user space can query it via EP_LOOKUP
ioctl.

DPL function has only 1 IN endpoint. The BAM transport (u_bam) module
is modified not to access OUT endpoint structure when it is NULL. The
BAM and BAM2BAM ports allocation is separated to return the newly
created port index. Remove the hard coded BAM-DMUX channel numbers
in u_bam and i_ctrl_qti modules and directly use the enums defined
in the BAM-DMUX header file.

Change-Id: I35e53eeeed5e71d52fa23e9c8326ef218c7c2fe8
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>