drm/i915: Replace the feature tests for BLT/BSD with ring init checks
When userspace asks whether the driver supports the BLT or BSD rings for
this chip, simply report whether those particular rings are initialised
v2: Use intel_ring_initialized()
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>