Revert "Documentation/gpu/meson: Remove link to meson_canvas.c"

This reverts commit a3f98bb2.

Patch "Documentation/gpu/meson: Remove link to meson_canvas.c" was
incorrectly applied on the wrong branch not containing the fixed
commit 2bf6b5b0 ("drm/meson: exclusively use the canvas provider module")
Acked-by: Sean Paul <sean@poorly.run>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190404144342.15238-1-narmstrong@baylibre.com

Documentation/gpu/meson.rst

@@ -42,6 +42,12 @@ Video Encoder
 .. kernel-doc:: drivers/gpu/drm/meson/meson_venc.c
    :doc: Video Encoder
 
+Video Canvas Management
+=======================
+
+.. kernel-doc:: drivers/gpu/drm/meson/meson_canvas.c
+   :doc: Canvas
+
 Video Clocks
 ============