drm/i915: Don't allocate extra ddb during async flip for DG2

In terms of async flip optimization we don't to allocate
extra ddb space, so lets skip it.

v2: - Extracted min ddb async flip check to separate function
      (Ville Syrjälä)
    - Used this function to prevent false positive WARN
      to be triggered(Ville Syrjälä)

v3: - Renamed dg2_need_min_ddb to need_min_ddb thus making
      it more universal.
    - Also used DISPLAY_VER instead of IS_DG2(Ville Syrjälä)
    - Use rate = 0 instead of just setting extra = 0, thus
      letting other planes to use extra ddb and avoiding WARN
      (Ville Syrjälä)

v4: - Renamed needs_min_ddb as s/needs/use/ to match
      the wm0 counterpart(Ville Syrjälä)
    - Added plane->async_flip check to use_min_ddb(now
      passing plane as a parameter to do that)(Ville Syrjälä)
    - Account for use_min_ddb also when calculating total data rate
      (Ville Syrjälä)

v5:
    - Use for_each_intel_plane_on_crtc instead of for_each_intel_plane_id
      to get plane->async_flip check and account for all planes(Ville Syrjälä)
    - Fix line wrapping(Ville Syrjälä)
    - Set plane data rate conditionally, avoiding on redundant assignment
      (Ville Syrjälä)
    - Removed redundant whitespace(Ville Syrjälä)
    - Handle use_min_ddb case in skl_plane_relative_data_rate instead of
      icl_get_total_relative_data_rate(Ville Syrjälä)

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220124090653.14547-2-stanislav.lisovskiy@intel.com