modesetting: Add support for headless display
In some Virtualization environments, a CRTC may not be available but a graphics device may still be present (/dev/dri/card0). In such situations, the modesetting DDX should still load Glamor (and DRI) and work in a "Headless" fashion.
Present's screen flip mode will handle the vblanks (and flips) in these situations.
Edited by Vivek Kasireddy