drm/i915/dp: Fix eDP max rate for display 11+

intel_dp_set_source_rates() calls intel_dp_is_edp(), which is unsafe to
use before intel_encoder->type is set. This causes incorrect max source
rate to be used for display 11+. On EHL and JSL, HBR3 is used instead of
HBR2, and on the other affected platforms, HBR2 is used instead of HBR3.

Move intel_dp_set_source_rates() to after intel_encoder->type is
set. Add comment to intel_dp_is_edp() describing unsafe usages. Cleanup
intel_dp_init_connector() while at it.

Note: The same change was originally added as commit 680c45c7
("drm/i915/dp: Correctly advertise HBR3 for GEN11+"), but later reverted
due to issues in CI in commit d3913019 ("Revert "drm/i915/dp:
Correctly advertise HBR3 for GEN11+"").

Cc: Uma Shankar <uma.shankar@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Matt Atwood <matthew.s.atwood@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Animesh Manna <animesh.manna@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210901160402.24816-2-animesh.manna@intel.com