drm/amd/display: Refactor DPP enum for backwards compatibility

[WHY]
Conflict for enum type in DPP source files.

[HOW]
Refactor DPP source files to resolve the enum conflicts.

Reviewed-by: Ilya Bakoulin <ilya.bakoulin@amd.com>
Reviewed-by: Martin Leung <martin.leung@amd.com>
Signed-off-by: Lohita Mudimela <lohita.mudimela@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>