drm/i915/cx0: Program vswing only for owned lanes

According to the BSpec, voltage swing programming should be done for
owned PHY lanes. Do not program a not-owned PHY lane.

BSpec: 74103, 74104
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230814131331.69516-5-gustavo.sousa@intel.com