drm/panfrost: Remove completed features still in TODO

There's a few features the driver supports which we forgot to remove, so
remove them now.

Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190802195727.1963-1-robh@kernel.org