drm/i915: move gmbus restore to i915_restore_display

Logically part of the display restore.

Note: This has been in place since the introduction of gmbus
support. The gmbus code also does the resets before transfers. Is this
really needed, or a historical accident?

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200910095227.9466-3-jani.nikula@intel.com