omapdrm: hdmi4: move hdmi4_core_powerdown_disable to hdmi_power_on_core()

Call hdmi4_core_powerdown_disable() in hdmi_power_on_core() to
power up the HDMI core (needed for CEC). The same call can now be dropped
in hdmi4_configure().

Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>