drm/i915: give more distinctive names to ring hangcheck action enums

The short lowercase names are bound to collide. The default warnings
don't even warn about shadowing.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>