Add USB host support based on the work of sztupy

Usb host driver and client/host otg changer interface modules

importing files from sgs2 host driver (this removes kevinh's fixes though)

added kevin's fixes to sgs2 host driver; added host_notify module

Change-Id: Ia538ac08269b5b7d8f696c5255e0278735f425d5

cleaned host start/shutdown code

forgot to commit these

Change-Id: Idee1e8499033032f8b426f9bc09bf6b71bca5e8e

allow changing of driver implementations while running

added initial support for dwc hot driver (not usable yet)
allow switching of drivers through sysfs

Fixes for Linaro toolchain