drm/i915: Disable DC states around GMBUS on GLK

commit 3488d0237f6364614f0c59d6d784bb79b11eeb92 upstream.

Prevent the DMC from destroying GMBUS transfers on GLK. GMBUS
lives in PG1 so DC off is all we need.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171208213739.16388-1-ville.syrjala@linux.intel.com


Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
(cherry picked from commit 156961ae7bdf6feb72778e8da83d321b273343fd)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>