drm/omap: HDMI: fix WP timings for ilace

The HDMI WP timings are not programmed correctly for interlace.

We need to halve the vertical timings when interlace is used, and double
the horizontal timings when pixel doubling is used.

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