drm/i915: Fix the training pattern debug print

Currently we claim to use TPS7 when using TPS4. That is just
confusing, so let's fix the debug print.

And while we're touching this let's add the customary
encoder id/name as well.

v2: Add MISSING_CASE() (Manasi)

Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210114205046.8247-2-ville.syrjala@linux.intel.com