drm/amd/display: Allow for sharing of some link and audio link functions

[Why&How]
Allow for sharing of some link and audio link functions by removing static
keyword from function definitions.
Expose those functions in the HWSEQ header.

Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Signed-off-by: Relja Vojvodic <rvojvodi@amd.com>
Signed-off-by: Ivan Lipski <ivan.lipski@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>