drm/ast: Use drm_aperture_remove_conflicting_pci_framebuffers

It's just open coded and matches.

Note that Thomas said that his version apparently failed for some
reason, but hey maybe we should try again.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Helge Deller <deller@gmx.de>
Cc: linux-fbdev@vger.kernel.org
Tested-by: Thomas Zimmmermann <tzimmermann@suse.de>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230111154112.90575-1-daniel.vetter@ffwll.ch