drm/amd/display: Allow for plane-less resource reservation

This change changes dc add plane logic to allow plane-less resource
reservation (pipe split).

If a free pipe_ctx (no plane_state attached) is the head pipe, and is
found with a bottom pipe attached, assign the plane to add on the bottom
pipe.

In addition, prepend dcn10 to dcn10-specific reset_back_end_for_pipe
and reset_hw_ctx_wrap

Signed-off-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>