usb: gadget: handle bam setup and cleanup for mbim in u_bam_dmux

When usb composition contains RMNET and MBIM functions, then
handle bam setup for mbim.
As RMNET and MBIM use same bam channel 8, In multi-function
usb compositions, RMNET binding happens before MBIM binding.
bam setup happens in binding operation. So if binding operation
happens for RMNET, then binding operation for MBIM is not required.

Depends on host selection of RMNET/MBIM function, same bam setup
will be used by one of functions RMNET/MBIM.

In non multi-function usb compositions where only RMNET or MBIM
present, RMNET or MBIM works as usual.

Change-Id: I5200d1a26726ee27e87a51404456232b09751b50
Signed-off-by: Prasadarao Durvasula <pdurvasu@codeaurora.org>
Signed-off-by: Sivasri Kumar Vanka <sivasri@codeaurora.org>