drm/amd/display: Enable RCO for HDMISTREAMCLK in DCN35

[Why & How]
Enable root clock optimization for HDMISTREAMCLK and only
disable it when it's actively being used.

Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Acked-by: Roman Li <roman.li@amd.com>
Signed-off-by: Daniel Miess <daniel.miess@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>