Totally cribbed from xf86-video-amdgpu/-radeon:

commit 560b7fe6dc66405762020f00e9a05918a36f3a17
Author: Michel Dänzer <michel.daenzer@amd.com>
Date:   Wed Nov 11 17:31:34 2015 +0900

    Rename Option "NoAccel" to "Accel"

Renaming the option removes the need for a double negation when forcing
acceleration on and is backwards compatible as the option parser
automagically handles the 'No' prefix.

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