[coreboot] SeaBIOS and USB UHCI keyboard support

[Kevin O'Connor]

The latest SeaBIOS git has preliminary support for USB keyboards.
I've tested this on qemu and on my epia-cn.

For info on obtaining SeaBIOS see:
http://www.coreboot.org/SeaBIOS

This support is still a little "rough" - help with testing would be
appreciated, but don't expect it to be fully functional.

Known issues:

- only uhci controllers are supported - no ohci (nor ehci)

- not all keys are mapped (eg, no numeric keypad)

- no keyboard auto-repeat

- no keyboard led support

- if one types fast, they may see dup keys or missing keys

- no hub support (keyboard must be directly attached)

- usb bandwidth is not optimized (no scheduling)

That said, I can control the SeaBIOS boot and navigate through a grub
console with my usb keyboard.

-Kevin