usb: dwc3-msm: Add support for default host mode if extcon absent

Currently the driver starts peripheral mode if DWC3 is dual role
capable but does not have extcon handle. But on some platforms
like automotive, the objective is to start host mode by default
if extcon is not present. Add required support for the same
based on DT property.

Change-Id: I397fe6aa9652e913e9ef9f8a82cc438706026405
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>