staging: most: hdm-usb: extend DCI access

This patch extends the direct communication interface ABI of the USB
network interface controller. It is needed to provide applications
arbitrary access to DCI registers and the ability to synchronize the
internal endpoint logic of the controller.

Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>