drm: bridge: dw-hdmi: Add Documentation on supported input formats

This patch adds a new DRM documentation entry and links to the input
format table added in the dw_hdmi header.

Reviewed-by: Archit Taneja <architt@codeaurora.org>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
diff --git a/Documentation/gpu/index.rst b/Documentation/gpu/index.rst
index e998ee0..d81c6ff 100644
--- a/Documentation/gpu/index.rst
+++ b/Documentation/gpu/index.rst
@@ -15,6 +15,7 @@
    vc4
    vga-switcheroo
    vgaarbiter
+   bridge/dw-hdmi
    todo
 
 .. only::  subproject and html