drm/qxl: Drop fbdev hwaccel flags

drm/qxl: Drop fbdev hwaccel flags

It's not accelarated, just system memory. Note we don't even need to
set the default flag since that's now always 0.

Note that originally qxl had acceleration support, but that was all
ripped out in

commit c0fe07aa50befe2e6e6525181e2080377a1c1494
Author: Gerd Hoffmann <kraxel@redhat.com>
Date:   Tue May 5 13:52:49 2015 +0200

    drm/qxl: rewrite framebuffer support

v2: Amend commit message a bit after irc chat with Dave.

Cc: Dave Airlie <airlied@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: virtualization@lists.linux-foundation.org
Acked-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170706125735.28299-4-daniel.vetter@ffwll.ch
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>