drm/amd/display: Fix DP2 link training failure with RCO

[Why]
When RCO is enabled for symclk32_le we get failures during
DP2 link traing compliance tests.

[How]
Break out symclk32_le RCO into a separate function that is
called for hpo when link is enabled/disabled.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Acked-by: Alan Liu <haoping.liu@amd.com>
Signed-off-by: Daniel Miess <daniel.miess@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>