drm/radeon: disable pll sharing for DP on DCE4.1

commit 9ef4e1d000a5b335fcebfcf8aef3405e59574c89 upstream.

Causes display problems.  We had already disabled
sharing for non-DP displays.

Based on a patch from:
Niels Ole Salscheider <niels_ole@salscheider-online.de>

bug:
https://bugzilla.kernel.org/show_bug.cgi?id=58121



Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>