drm/i915: Fix PCH reference clock for FDI on HSW/BDW

drm/i915: Fix PCH reference clock for FDI on HSW/BDW

The change to skip the PCH reference initialization during fastboot
did end up breaking FDI. To fix that let's try to do the PCH reference
init whenever we're disabling a DPLL that was using said reference
previously.

Cc: stable@vger.kernel.org
Tested-by: Andrija <akijo97@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112084
Fixes: b16c7ed95caf ("drm/i915: Do not touch the PCH SSC reference if a PLL is using it")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191022185643.1483-1-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>