This adds more complete handling of VDMs and registration of
partner alternate modes, and introduces callbacks for
alternate mode operations.

Only DFP role is supported for now.
Signed-off-by: NHeikki Krogerus <heikki.krogerus@linux.intel.com>
Tested-by: NHans de Goede <hdegoede@redhat.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>