Initial support for Nook Color host mode.

This is pretty hackish at the moment, but seems to work mostly well.
Known quirk: if you disable host mode while some devices are still attached,
they won't be disconnected - perhaps need to call for disconnect in this case.

Change config: enable usb host support

Certain usb devices enabled too, like HID, UVC, usb masstorage, usb serial.

ipv6 disabled to keep the kernel size under 3M

Added syfs output of charger status. Also ability of power draw control.

Changed to usb host mode on Nook:

Ability to request externally driven vbus (by battery or external source).
Default to externally driven vbus when external power is connected at
vbus request time.
Don't try to do anything with vbus when a change comes for the same mode
we are already in.

Defconfig: More USB input device drivers