drm/i915: Check pipe active state in {planes,vrr}_{enabling,disabling}()

{planes,vrr}_{enabling,disabling}() are supposed to indicate
whether the specific hardware feature is supposed to be enabling
or disabling. That can only makes sense if the pipe is active
overall. So check for that before we go poking at the hardware.

I think we're semi-safe currently on due to:
- intel_pre_plane_update() doesn't get called when the pipe
  was not-active prior to the commit, but this is actually a bug.
  This saves vrr_disabling(), and vrr_enabling() is called from
  deeper down where we have already checked hw.active.
- active_planes mirrors the crtc's hw.active

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231121054324.9988-2-ville.syrjala@linux.intel.com