drm/i915: Split a setting of MSA to MST and SST

The setting of MSA is done by the DDI .pre_enable() hook. And when we are
using MST, the MSA is only set to first mst stream by calling of
DDI .pre_eanble() hook. It raies issues to non-first mst streams.
Wrong MSA or missed MSA packets might show scrambled screen or wrong
screen.

This splits a setting of MSA to MST and SST cases. And In the MST case it
will call a setting of MSA after an allocating of Virtual Channel from
MST encoder pre_enable callback.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112212
Fixes: 0c06fa15 ("drm/i915/dp: Add support of BT.2020 Colorimetry to DP MSA")
Fixes: d4a415dc

 ("drm/i915: Fix MST oops due to MSA changes")
Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191106212636.502471-1-gwan-gyeong.mun@intel.com
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
[vsyrjala: nuke spurious newline]
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
(cherry picked from commit bd8c9cca

)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191113125241.20547-1-ville.syrjala@linux.intel.com