drm/amd/display: Update DCN321 hook that deals with pipe aquire

DCN provides a hook to check if we can have a new pipe allocation based
on some DC constraints. If the current configuration supports the new
pipe request, DC updates its context; otherwise, it will keep the same
configuration. This behavior is similar across multiple ASICs, and for
this reason, we reused DCN20 on DCN321. However, this DCN32x has some
peculiarities which require its function to avoid weird pipe split
issues. This commit update this issue by using
dcn32_acquire_idle_pipe_for_head_pipe_in_layer instead of
dcn20_acquire_idle_pipe_for_layer.

Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>