drm/i915/tgl: PSR link standby is not supported anymore

According to BSpc if link standby is set on TGL+, PSR will not be
enabled. Vendors should not use panels that requires link standby and
even if they do, panel should assert a PSR error that will cause PSR to
be disabled.

BSpec: 50434
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Anshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190823082055.5992-8-lucas.demarchi@intel.com