modesetting: find the first compatible dri device as default

This change replaces the default "/dev/dri/card0" by a loop which searches for the first compatible device.

This change avoids the error below which happens on some ARM boards:

(EE) No devices detected.
(EE)
Fatal server error:
(EE) no screens found(EE)
(EE)

Signed-off-by: Patrick Lerda patrick9876@free.fr