drm/amd/display: Unify fast update classification paths

drm/amd/display: Unify fast update classification paths

[Why]
The dc_fast_update intermediate struct created code duplication and
complexity with multiple classification paths (populate_fast_updates,
fast_nonaddr_updates_exist, full_update_required). This refactoring
simplifies the update classification system by consolidating to a
single path while maintaining compatibility and adding comprehensive
test coverage for fast sequence functionality.

[How]
Remove entire dc_fast_update struct and associated helper functions:
- populate_fast_updates
- fast_nonaddr_updates_exist
- full_update_required
and
- Refactor check_update_surfaces_for_stream as the
  single classification path with explicit handling for func_shaper,
  lut3d_func, cursor_csc_color_matrix_change and
  scaler_sharpener_update.
- Add reserved bitfields to surface_update_flags and
  stream_update_flags unions for completeness guards.
- Extract dc_check_address_only_update and
  dc_check_update_surfaces_for_stream as public.
- Add comprehensive test coverage with parameterized tests for all
  FAST flags, update classification tests for MED/FULL paths,
  and completeness guard tests.

Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Signed-off-by: Rafal Ostrowski <rafal.ostrowski@amd.com>
Signed-off-by: Tom Chung <chiahsuan.chung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>