drm/i915: Initialize eDP source rates after per-panel VBT parsing

We'll need to know the VBT panel_type before we can determine the
maximum link rate for eDP. To that end move
intel_dp_set_source_rates() & co. to be called after the per-panel
VBT parsing has been done.

intel_dp_mst_encoder_init() depends on the source rates so we'll
have to do it a bit later as well.

v2: Fix the intel_dp_mst_encoder_init() oops

Reviewed-by: Jani Nikula <jani.nikula@intel.com> #v1
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220603165841.15481-1-ville.syrjala@linux.intel.com