OMAP4: TWL: add vdda_hdmi_dac regulator supply

HDMI requires vdda_hdmi_dac (vdac) power for operation. The regulator,
or the regulator supplying the vdac, has been enabled by default and
things have worked without the HDMI driver enabling the vdac.

I encountered the problem when implementing HDMI device tree support,
where the regulator was not enabled by default.

This patch adds the vdda_hdmi_dac to twl-common.c so that the HDMI
driver can use it.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>