drm/i915: Fix PLL state check for gmch platforms

GMCH DPLL state check was mistakenly removed in
commit 87fc875a ("drm/i915/dg2: Skip shared DPLL handling").
Bring it back.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240209183809.16887-2-ville.syrjala@linux.intel.com


Reviewed-by: Mika Kahola <mika.kahola@intel.com>