drm/omap: HDMI: support double-pixel pixel clock

We need double-pixel mode (pixel repetition) for interlace modes. This
patch adds the necessary support to HDMI to double the pixel clock when
double-pixel mode is used.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>