drm/i915/display: Warn on use_dsb in non-dsb pipe update functions

Add drm_WARN_ON(use_dsb) into commit_pipe_{pre,post}_planes() and
intel_pipe_update_{start,end}() as they are not supposed to get called on
non-dsb updates.

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250213064804.2077127-9-jouni.hogander@intel.com