usb: dwc3: Change to simulate VBUS without extcon/PMI

On targets that does not have any mechanism for VBUS
and ID notifications, simulate a VBUS connect to put
the core in peripheral mode by default.

Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>
Change-Id: I951af6d98820bc2ee1bd8f7d3affa3832b4695f9