usb: xhci: dwc3: Adding reset delay requirement as per dwc3 databook

As per dwc3 databook, delay is required before taking the core out of reset.
This delay is required so that the PHY are stable, and then we can take core
out of reset.

Reference is taken from linux dwc3 code, file: drivers/usb/dwc3/core.c.

Signed-off-by: Sriram Dash <sriram.dash@freescale.com>
Signed-off-by: Rajesh Bhagat <rajesh.bhagat@freescale.com>