APPLIED: ARM: rpi: only set usbethaddr on relevant systems

Model A and CM RPis don't have an on-board USB Ethernet device. Hence,
there's no point setting $usbethaddr based on the device fuses. Use the
model detection code to gate this. Note that the fuses are actually
programmed even on those devices though.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
---
This depends on the following patches that I sent earlier:
ARM: rpi_b: detect board revision
ARM: rpi: rename rpi_b to rpi
APPLIED: ARM: rpi: support model A+

Add a board rev entry for the new model A+, and augment the board
rev error handling code to be a bit more verbose.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
APPLIED: ARM: rpi: consolidate board rev error checking

Create a fake model table entry with default values, so we can error
check the board rev value once when querying it from the firmware, rather
than error-checking for invalid board rev values every time the model
table is used.

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>
BROKEN: ARM: rpi: enable USB keyboard

This will allow the user to interact with U-Boot without a serial
console. Unfortunately this doesn't work at present; while USB Mass
Storage devices appear to work fine with U-Boot's DWC2 driver, USB
keyboard devices don't:-(

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
Revert "BROKEN: ARM: rpi: enable USB keyboard"

This reverts commit 5504a530fe24b63489e49531f7d2a273b6f99fae.