drm/i915/display: Set source_support even if panel do not support PSR

This will set the right value of source_support when the port
encoder/port supports PSR but sink don't.

This change will also be needed in future for panel replay as psr
struct needs to be initialized even if disconnected or current sink
don't support PSR.

Cc: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210209181439.215104-4-jose.souza@intel.com