usb: add driver for Synopsis DWC2 USB IP block

This is the USB host controller used on the Raspbery Pi.

swarren changelog:
* Fixed prototype of usb_lowlevel_init() to match upstream change.
* Fixed a number of unused variable warnings.
* Replaced license headers with SPDX tags.
* Renamed files DWC -> DWC2 to make it clear which HW it's for.
* Many hundreds of checkpatch fixes.

Signed-off-by: Oleksandr Tymoshenko <gonzo@bluezbox.com>
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
---
I've fixed all the checkpatch errors. There are hundreds of warnings left.
Still, I figured it was a good idea to post the patch for review of any
other aspects.
ARM: rpi_b: enable USB features in config

* Enable USB HW driver
* Don't disable USB-related commands any more
* Add USB-related support to bootcmd

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
ARM: rpi_b: query internal MAC address from firmware

The built-in SMSC 95xx chip doesn't know its own MAC address. Instead,
we must query it from the VC firmware; it's probably encoded in fuses
on the BCM2835.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
LOCAL: ARM: rpi_b: add script to chain-load U-Boot over DHCP/TFTP

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>