OMAPDSS: HDMI: Use our own omap_video_timings field when setting interface timings

The hdmi driver currently updates only the 'code' member of hdmi_config when
the op omapdss_hdmi_display_set_timing() is called by the hdmi panel driver.
The 'timing' field of hdmi_config is updated only when hdmi_power_on is called.
It makes more sense to configure the whole hdmi_config field in the set_timing
op called by the panel driver. This way, we don't need to call both functions
to ensure that our hdmi_config is configured correctly. Also, we don't need to
calculate hdmi_config during hdmi_power_on, or rely on the omap_video_timings
in the panel's omap_dss_device struct.

The default timings of the hdmi panel are represented in a cleaner form. Since
the hdmi output is now configured by it's own copy of timings (in
hdmi.ip_data.cfg), the panel driver needs to set it to a valid value before
enabling hdmi output. We now call omapdss_hdmi_set_timing() before enabling
hdmi output, this is done to atleast have the hdmi output configured to the
panel's default timings if the DSS user didn't call panel driver's set_timings()
op explicitly.

Signed-off-by: Archit Taneja <archit@ti.com>