Do not consider disabled crtc anymore when looking for xf86crtc covering drawable.

This is commit is removing obsolete switch done in

xf86-video-ati at sha 61d0aec40e2521488c2fe43e7a6823e5c87d94d7:  video: add option to include disabled CRTCs in best CRTC search
This is not required anymore as with commit done in
xorg-server at sha 5c5c1b77982a9af7279a90bc3c2be48adaa9c778:     present: Add Present extension
That in case of lack of crtc is using fake_crtc with render 1Hz frequency

When consider_disabled is removed then amdgpu_pick_best_crtc is doing the same what rr_crtc_covering_box is doing
so it can be reimplemented to reuse that function.

Signed-off-by: Łukasz Spintzyk <lukasz.spintzyk@synaptics.com>
Signed-off-by: Shashank Sharma <contactshashanksharma@gmail.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
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