drm/i915: Remove the encoder update_prepare()/complete() hooks

The encoder update_prepare()/complete() hooks were added to hold a
TC port link reference for all outputs in the atomic state around the
whole modeset enable sequence - thus locking the ports' TC mode - and
set the TBT/DP-alt PLL type corresponding to the current TC mode.

Since nothing depends on the PLL selection before/after then encoder's
pre_pll_enable/post_pll_disable hooks are called, the above steps can be
moved to these hooks, so do that and remove the
update_prepare()/complete() hooks.

Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230323142035.1432621-30-imre.deak@intel.com