docs: driver-api: Update Surface Aggregator user-space interface documentation

Update the controller-device user-space interface (cdev) documentation
for the newly introduced IOCTLs and event interface.

Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20210604134755.535590-8-luzmaximilian@gmail.com


Signed-off-by: Hans de Goede <hdegoede@redhat.com>