drm/sti: Try to fix up the tvout possible clones

The current possible_clones setup doesn't look sensible. I'm assuming
the 0 and 1 are supposed to refer to the indexes of the hdmi and hda
encoders? So it kinda looks like we want hda+hdmi cloning, but then
dvo also claims to be cloneable with hdmi, but hdmi won't recipricate.

Benjamin tells me all encoders should be cloneable with each other,
so let's fix up the masks to indicate that.

Cc: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Cc: Vincent Abriou <vincent.abriou@st.com>
Acked-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190708162048.4286-5-ville.syrjala@linux.intel.com