drm/i915: Only sanitize GEM from late suspend

During testing we encounter a conflict between SUSPEND_TEST_DEVICES and
disabling reset (gem_eio/suspend). This results in the device continuing
on without being reset, but since it has gone through HW sanitization to
account for the suspend/resume cycle, we have to assume the device has
been reset to its defaults. A simple way around this is to skip the
sanitize phase for SUSPEND_TEST_DEVICES by moving it to suspend-late.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180531082246.9763-4-chris@chris-wilson.co.uk