drm/i915: Kick waiters on resetting legacy rings

For reasons unknown, interrupts following a reset do not arrive, but
this can be papered over by kicking any waiter and peeking at the
breadcrumbs following the reset.

Testcase: igt/gem_eio/reset-stress
References: https://bugs.freedesktop.org/show_bug.cgi?id=105957


Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180730075351.15569-2-chris@chris-wilson.co.uk