drm/bridge: ti-sn65dsi86: Read EDID blob over DDC

Use the DDC connection to read the EDID from the eDP panel instead of
relying on the panel to tell us the modes.

Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
Cc: Jonas Karlman <jonas@kwiboo.se>
Cc: Jernej Skrabec <jernej.skrabec@siol.net>
Cc: Sean Paul <seanpaul@chromium.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201102181144.3469197-4-swboyd@chromium.org