drm/omap: dss: hdmi: Rename hdmi_display_(set|check)_timing() functions

The two functions implement the .set_timings() and .check_timings()
operations. Rename them to hdmi_disply_set_timings() and
hdmi_display_check_timings() respectively to match the operations names
and make searching the source code easier.

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>