ARM: rpi_b: load /uEnv.txt from MMC at startup

The Pi has no flash to store an environment in the usual fashion. However,
the user may wish to customize the environment. We know that the SD card
must be present, since that's where the boot ROM has loaded U-Boot from.
So, load uEnv.txt from there early during boot. This allows the user to
e.g. customize boot_targets, in order to automatically select network
boot.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
ARM: rpi_b: rework boot scripts, enable sysboot

Rework rpi_b's bootcmd (and sub-commands) to match Tegra's bootcmd as
much as possible. This will aid in a future patch which will create a
common header e.g. config_distro_bootcmd.h.

While at it, enable booting from extlinux.conf using the sysboot command.

The iteration and componentization currently makes a little more sense
for Tegra than RPi, but I'd still like to keep the two as similar as
possible. USB and networking support is coming to the RPi in due course,
and it'll all make more sense then anyway.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
DWC2: add host driver from Oleksandr's branch

swarren changelog:
* Fixed prototype of usb_lowlevel_init() to match upstream change.

TODO:
* Rename dwc -> dwc2

Signed-off-by: Oleksandr Tymoshenko <gonzo@bluezbox.com>
Signed-off-by: Stephen Warren <swarren@wwdotorg.org>
DWC2: fix unused variables

TODO: Squash into previous commit.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
DWC2: rename from DWC

TODO: Squash into previous commit.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
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>
HACK: SMSC95XX: hard-code Ethernet address

TODO: get this from firmware instead

Signed-off-by: Oleksandr Tymoshenko <gonzo@bluezbox.com>
[swarren: extracted from a larger patch]
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>