drm/imx: dw_hdmi-imx: move initialization into probe

Parts of the initialization that do not require the drm device can be
done once during probe instead of possibly multiple times during bind.
The bind function only creates the encoder and attaches the bridge.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>