drm/print: drop include seq_file.h

Never include where a forward declaration will suffice.

Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240410141434.157908-2-jani.nikula@intel.com
Link: https://patchwork.freedesktop.org/patch/msgid/20240422121011.4133236-2-jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>