drm/i915: Enable/disable shared dplls just the once for joined pipes

drm/i915: Enable/disable shared dplls just the once for joined pipes

Currently we loop over all joined pipes and enable/disable the
shared dplls for each. We don't really have to do that since
all joined pipes will be using the same dpll. So let's just do
the enable/disable once for the whole set of joined pipes.
We can still keep tracking the dpll active set as pipes as long
as we remember to flip the bits for all the joined pipes on one go.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250310183528.3203-1-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>