drm/i915: Move the conditional seqno query into the tracepoint

We only wish to know the value of seqno when emitting the tracepoint, so
move the query from a parameter to the macro to inside the conditional
macro body so that the query is only evaluated when required.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>