drm/amd/display: Allow reuse of of DCN4x code

Remove the static qualifier to make it available for code sharing
with other components.

Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Signed-off-by: Dmytro <dmytro.laktyushkin@amd.com>
Signed-off-by: Charlene Liu <Charlene.Liu@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>