drm/i915: Remove redudant wait for each engine to idle from seqno wrap

drm/i915: Remove redudant wait for each engine to idle from seqno wrap

Having added the wait upon each engine to idle into the central
i915_gem_wait_for_idle(), we can remove the now redundant wait from
reset_all_global_seqno(). This has the advantage of removing the late
detection of an error (an engine still busy) which left the seqno reset
only partially complete (though it should be safe enough!).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170330145041.9005-5-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>