USB: dwc3: Implement revised initialization sequence

Revise initialization and power-on routines to
be more consistent with recommended sequences.
Since some of the same sequences are repeated during
USB cable reconnection and exiting from power collapse,
consolidate these into common routines to avoid duplicated code.

Change-Id: I99856ac2ff01daa75b7e6d5a584c1b314402aa03
Signed-off-by: Mayank Rana <mrana@codeaurora.org>