drm/amd/display: define link res and make it accessible to all link interfaces

drm/amd/display: define link res and make it accessible to all link interfaces

[why]
There will be a series of re-arch changes in Link Resource Management.
They are more and more muxable link resource objects and the resource is
insufficient for a one to one allocation to all links created.
Therefore a link resource sharing logic is required to determine which
link should use certain link resource.

This commit is the first one in this series that starts by defining a
link resource struct, this struct will be available to all interfaces
that need to perform link programming sequence.

In later commits, we will granduately decouple link resource objects out
of dc link. So instead of access a link resource from dc link. Current
link's resource can be accessible through pipe_ctx->link_res during
commit, or by calling  dc_link_get_cur_link_res function with current
link passed in after commit.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@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>