drm/amd/display: Send s0i2_rdy in stream_count == 0 optimization

[Why]
Otherwise SMU won't mark Display as idle when trying to perform s2idle.

[How]
Mark the bit in the dcn31 codepath, doesn't apply to older ASIC.

It needed to be split from phy refclk off to prevent entering s2idle
when PSR was engaged but driver was not ready.

Fixes: 118a3315 ("drm/amd/display: Add DCN3.1 clock manager support")

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Eric Yang <Eric.Yang2@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>