drm/omap: Move DSI debugfs clocks dump to dsi%u_clks files

The DSI clocks are dumped in the DSS-level debugfs clocks file. This
complicates the implementation as the DSI private data has to be looked
up through the outputs list. Simplify it by creating two debugfs files,
dsi1_clks and dsi2_clks, to dump the DSI clocks.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>