drm/amd/display: Enable physymclk RCO

[Why]
Enable the last of the RCO options for dcn35

[How]
Breakout RCO from dccg35_set_physymclk so that
physymclk RCO can be set in dccg_init without
disabling physymclk

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Jun Lei <jun.lei@amd.com>
Acked-by: Hersen Wu <hersenxs.wu@amd.com>
Signed-off-by: Daniel Miess <daniel.miess@amd.com>
Signed-off-by: Hersen Wu <hersenxs.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>