drm/qxl: use kernel mode db

Add all standard modes from the kernel's video mode data base.
Keep a few non-standard modes in the qxl mode list.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20190118122020.27596-23-kraxel@redhat.com