add to accelerant api to support managing multiple montors

[kallisti5]

We could add to the accelerant API to enable the app_server to detect the number of displays on a card, and tell the accelerant instance which display to focus on.

That would mean that the app_server would spawn one accelerant for every attached monitor. (we would need to throughly go over locking in each video card driver however)

This ticket is to track the progression of this idea. As these changes may bump the API, *NO* diffs attached should be pushed upstream until a final decision is reached.

We also need to decide if such a change is a pre-or post R1 change. We could start laying the groundwork pre-R1 so the changes post-R1 would be minimal. (however, that needs some discussion). Without a change to the accelerant api, Haiku will not support multiple displays at R1.

[kallisti5]

revision 1 of the proposed changes, likely needs expanding.

[kallisti5]

in the 1st revision patch, connector_type and encoder_type are populated by the macros in ​http://cgit.haiku-os.org/haiku/tree/headers/private/graphics/common/video_configuration.h

[kallisti5]

revision 2 of the proposed changes, added hook to set display to focus on.