drm/i915: Stop sleeping from inside gen6_bsd_submit_request()

submit_request() is called from an atomic context, it's not allowed to
sleep. We have to be careful in our parameters to
intel_uncore_wait_for_register() to limit ourselves to the atomic wait
loop and not incur the wrath of our warnings.

Fixes: 6976e74b ("drm/i915: Don't allow overuse of __intel_wait_for_register_fw()")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170410143807.22725-1-chris@chris-wilson.co.uk
Link: http://patchwork.freedesktop.org/patch/msgid/20170411101340.31994-2-chris@chris-wilson.co.uk


Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>