drm/i915/ddi: enable ACT handling for 128b/132b SST

Add ACT handling for 128b/132b SST enable/disable.

This is preparation for enabling 128b/132b SST. This path is not
reachable yet.

v2:
- Check for !is_hdmi (Imre)
- Add disable sequence (Imre)

Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/b0226471f9445d988917cee49dbbd93a1493f3c7.1735912293.git.jani.nikula@intel.com