drm/amd/display: add more link_hwss types and method to decide which one

[why]
as we add more link_hwss we are making a generic way to determine which type
of link_hwss we should use.
Later on we may think of introduce a link policy layer. it could be a thin layer
that decide the type of link_hwss we use. So instead of passing in link and link_res
we can just pass in link_policy and swtich based on link_policy->get_link_hwss_type.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>