drm/meson: exclusively use the canvas provider module

Now that the DMC register range is no longer in the bindings, remove any
mention towards it and exclusively use the meson-canvas module.

Signed-off-by: Maxime Jourdan <mjourdan@baylibre.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190311105144.7276-3-mjourdan@baylibre.com