drm/amd/display: Update dc_tiling_info union to structure

[WHY]
The `dc_tiling_info` union previously did not have a field to
specify the active GFX format, assuming only one format would
be used per DCN version. from DCN4+, support for switching
between different GFX formats is introduced, requiring a way
to track which format is currently in use.

[HOW]
Updated the `dc_tiling_info` union to include a new field that
explicitly indicates the currently used GFX format.
This allows the system to determine the active GFX format
and take the correct programming path accordingly.

[Description]
The union `dc_tiling_info` has been updated to support multiple
GFX formats by adding a new field for identifying the active format.
This update ensures that the correct programming path is followed
based on the selected format. All references to `dc_tiling_info`
in the codebase have been updated to reflect the new structure.

Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Signed-off-by: Karthi Kandasamy <karthi.kandasamy@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>