drm/i915/selftests: Skip all request selftests when wedged

If the GPU is irrecoverably wedge, we cannot submit any request and so
all of the request selftests will expectedly fail. Skip over them.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180706065332.15214-5-chris@chris-wilson.co.uk