ARM: rpi_b: set $fdtfile in default environment

U-Boot names the Raspberry Pi board rpi_b. This means that the common
expression for DTB filename ${soc}-${board}.dtb expands to
bcm2835-rpi_b.dtb. However, the DTB generated by the Linux kernel is
bcm2835-rpi-b.dtb. Set $fdtfile in U-Boot's environment so that scripts
look for the correct DTB filename.

An alternative would be to rename the U-Boot board to rpi-b. However,
that change would be far more invasive, and end up affecting users (i.e
they'd have to change their U-Boot build commands).

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
ARM: bcm2835: config.mk isn't needed

The entries in config.mk were needed so that U-Boot could be built
with an old version of the Raspberry Pi Foundation's toolchain. Without
them, the build would error out with:

...-ld: error: .../libgcc.a(_bswapsi2.o) uses VFP register arguments,
u-boot does not

However, none of the 3 toolchains in the latest version of their
tools.git, nor the Ubuntu/Linaro ARM compilers in at least Ubuntu Quantal
or Saucy, need these options set in order to compile a working U-Boot.
Hence, remove the options for simplicity.

Reported-by: Tom Rini <trini@ti.com>
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
DWC2 USB support 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>
ARM: rpi_b: enable USB features in config

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

TODO: get this from firmware instead
ARM: rpi_b: hack in bootcmd from Tegra

TODO:
a) Split this out into common file to share with Tegra and other SoCs.
b) Enable all the syslinux/pxe stuff too.

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