OMAPDSS: Add DSS feature for HDMI MCLK for audio

Certain OMAP4 revisions (i.e., 4430 ES2.3, 4460, and 4470) use
a pseudo clock (generated from the TMDS clock), MCLK, to drive the
generation of Audio Clock Regeneration packets. Other devices
(i.e., 4430 ES2.[0,2]) use the TMDS clock directly.

This patch adds a new DSS feature for MCLK support. It also rearranges
the omap_dss_features structures to reflect the devices supporting it.

Signed-off-by: Ricardo Neri <ricardo.neri@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>