drm/vc4: hdmi: Enable the scrambler on reconnection

If we have a state already and disconnect/reconnect the display, the
SCDC messages won't be sent again since we didn't go through a disable /
enable cycle.

In order to fix this, let's call the vc4_hdmi_enable_scrambling function
in the detect callback if there is a mode and it needs the scrambler to
be enabled.

Fixes: 74465b84 ("drm/vc4: hdmi: Enable the scrambler")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>