drm: Fix TODO list mentioning non-KMS drivers

Non-KMS drivers have been removed from DRM. Update the TODO list
accordingly.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: a276afc1 ("drm: Remove some obsolete drm pciids(tdfx, mga, i810, savage, r128, sis, via)")
Cc: Cai Huoqing <cai.huoqing@linux.dev>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v6.3+
Cc: linux-doc@vger.kernel.org
Reviewed-by: David Airlie <airlied@gmail.com>
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231122122449.11588-3-tzimmermann@suse.de