Add USB host ethernet adapter support

This adds support for using USB Ethernet dongles in host mode. This is just
the framework - drivers will come later. A new config option called
CONFIG_USB_HOST_ETHER can be defined in board config files to switch this
on.

The was originally written by NVIDIA and was cleaned up for release by the
Chromium authors.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/README.usb b/doc/README.usb
index b3bcb91..9aa4f62 100644
--- a/doc/README.usb
+++ b/doc/README.usb
@@ -28,7 +28,8 @@
 The USB support is implemented on the base of the UHCI Host
 controller.
 
-Currently supported are USB Hubs, USB Keyboards and USB Floppys.
+Currently supported are USB Hubs, USB Keyboards, USB Floppys, USB
+flash sticks and USB network adaptors.
 Tested with a TEAC Floppy TEAC FD-05PUB and Chicony KU-8933 Keyboard.
 
 How it works:
@@ -78,3 +79,4 @@
 		    if using CONFIG_CMD_USB
 CONFIG_USB_KEYBOARD enables the USB Keyboard
 CONFIG_USB_STORAGE  enables the USB storage devices
+CONFIG_USB_HOST_ETHER	enables USB ethernet dongle support