usb: gadget: Rmnet: Add support for Rmnet over DWC3 controller

Rmnet is a USB tethering interface that is using HW accelerated
path via BAM2BAM.

This change adds the required support to enable the BAM2BAM
path for ECM also on DWC3 new USB controller.

Change-Id: I65a806fb25261548515d91a8f78d37bf8eb8d14f
Signed-off-by: Ido Shayevitz <idos@codeaurora.org>