usb: dwc3-msm: consolidate DBM driver

Currently the DBM module registers a separate platform driver that
probes the DBM device separately than that of the dwc3-msm device
and driver. Since DBM is useless outside of dwc3-msm, it need not
be an independent driver and can be consolidated into the dwc3-msm
module directly. This eliminates a possible probe deferral in case
the devices probe in a certain order. Reassign the DT bindings to
the dwc3-msm node itself.

Change-Id: I5ec8820398fdfce626e15f2e75027fc02b4e5da5
Signed-off-by: Jack Pham <jackp@codeaurora.org>