drm/i915: Configure TRANSCONF just the once with bigjoiner

Let's not configure the single transcoder's TRANSCONF multiple
times with bigjoiner. No real harm I suppose but since we already
have the bigjoiner if statement directly above might as well suck
this in there and skip the redundant programming.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210913144440.23008-11-ville.syrjala@linux.intel.com


Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>