[randr-1.3] ramdac awareness

[Maarten Maathuis]

I can be short about this, the current infrastructure is only crtc
aware, this is not enough, since there can be 3 ramdac's and 2 crtc's
(for nvidia hardware) and restrictions on who gets what. So a property
similar to what crtc's have (a crtc_mask) would be greatly
appreciated. Currently i'm working around this, but this has
limitations.

Sincerely,

Maarten Maathuis.