drm/i915/psr: Unify PSR pre/post plane update hooks

drm/i915/psr: Unify PSR pre/post plane update hooks

intel_psr_pre_plane_update() operates on a per-crtc level, whereas
intel_psr_post_plane_update() operates on the whole atomic commit,
for no real reason that I can see. Adjust intel_psr_post_plane_update()
to match the intel_psr_pre_plane_update() approach.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231004155607.7719-2-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>