OMAPDSS: HDMI: Remove custom hdmi_video_timings struct

The hdmi CEA and VESA timings were represented by the struct hdmi_video_timings,
omap_video_timings couldn't be used as it didn't contain the fields hsync/vsync
polarities and interlaced/progressive information.

Remove hdmi_video_timings, and use omap_video_timings instead.

Cc: Mythri P K <mythripk@ti.com>
Signed-off-by: Archit Taneja <archit@ti.com>