drm/i915/edp: postpone MSO init until after EDID read

MSO will require segment pixel overlap information from the
EDID. Postpone MSO init until after we've read and cached the EDID.

Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/7a360fca01be0f971337b3635f4e4752922ffebe.1630419362.git.jani.nikula@intel.com