Chris Wilson authored Sep 13, 2015 and Adam Jackson committed Oct 20, 2015

Before we change the state (e.g. adding a mode or applying one to an
output), we query the screen resources for the right identifiers. This
should only use the current information rather than force a reprobe on
all hardware - not only can that reprobe be very slow (e.g. EDID
timeouts on the order of seconds), but it may perturb the setup that the
user is trying to configure.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>