drm/i915/guc: Reorder __i915_guc_submit to reduce spinlock holdtime

A couple of operations, the flushes and the tracepoint, do not require
serialisation by client->wq_lock, so move them before we take it.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170228112803.11646-3-chris@chris-wilson.co.uk


Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>