drm/i915/gt: Do not suspend bonded requests if one hangs

Treat the dependency between bonded requests as weak and leave the
remainder of the pair on the GPU if one hangs.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210120121718.26435-1-chris@chris-wilson.co.uk