OMAPDSS: HDMI: use core power on/off with edid & detect

This patch makes use of the hdmi_power_[on|off]_core() functions added
in the previous patch. The functions are used when reading EDID or
detecting if a monitor is connected.

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