drm/i915/cx0: Add MTL+ .update_active_dpll hook

drm/i915/cx0: Add MTL+ .update_active_dpll hook

Add .update_active_dpll function pointer to support
dpll framework. Reuse ICL function pointer.

v2: Add check for !HAS_LT_PHY (Suraj)
v3: Remove the incorrect !HAS_LT_PHY condition and
    check for existing dpll_mgr

Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com> # v1
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://lore.kernel.org/r/20251118132830.2584422-1-mika.kahola@intel.com