drm/i915: Combine reset_all_global_seqno() loops into one

We can merge the pair of loops over the engines and their timelines into
a single loop, making it easier to read and more consistent with the
commentary.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170330145041.9005-6-chris@chris-wilson.co.uk


Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>