drm/i915: reintroduce VLV/CHV PFI programming power domain workaround

drm/i915: reintroduce VLV/CHV PFI programming power domain workaround

There are still cases on these platforms where an attempt is made to
configure the CDCLK while the power domain is off, like when coming back
from a suspend.  So the workaround below is still needed.

This effectively reverts commit ca8bf0be5612 ("drm/i915: Nuke the
VLV/CHV PFI programming power domain workaround").

Cc: stable@vger.kernel.org
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101517
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170628210605.4994-1-krisman@collabora.co.uk
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>