With UCSI the alternate modes, just like everything else
related to USB Type-C connectors, are handled in firmware.
The operating system can see the status and is allowed to
request certain things, for example entering and exiting the
modes, but the support for alternate modes is very limited
in UCSI. The feature is also optional, which means that even
when the platform supports alternate modes, the operating
system may not be even made aware of them.

UCSI does not support direct VDM reading or writing.
Instead, alternate modes can be entered and exited using a
single custom command which takes also an optional SVID
specific configuration value as parameter. That means every
supported alternate mode has to be handled separately in
UCSI driver.

This commit does not include support for any specific
alternate mode. The discovered alternate modes are now
registered, but binding a driver to an alternate mode will
not be possible until support for that alternate mode is
added to the UCSI driver.
Tested-by: Ajay Gupta <ajayg@nvidia.com>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>