usb: Add USB device controller header file

Add USB device controller header file containing the USB device
controller APIs. All device controller drivers should implement the
APIs described in this file.

Change-Id: I14443a5286bbc2faddbd6420ce1668acb183cd2e
Signed-off-by: Adrian Bradianu <adrian.bradianu@windriver.com>
Signed-off-by: Daniel Leung <daniel.leung@intel.com>
Signed-off-by: Jesus Sanchez-Palencia <jesus.sanchez-palencia@intel.com>