Flush according to what gen11 expects when writing
breadcrumbs. As only the seqnowrite + flush differs
between engine and gens, enclose the footer to
helper.

v2: avoid problem of sane local naming by not using them

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NMika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190815094929.358-1-mika.kuoppala@linux.intel.com