drm/i915: Add missing ring_mask to Pineview

drm/i915: Add missing ring_mask to Pineview

It appears that we never told Pineview it has a RENDER_RING. This was
all fine until we started using the ring_mask for determining all the
available rings to initialise for legacy ringbuffer submission in commit
88d2ba2e95c8 ("drm/i915: Unify engine init loop"). Though really it is a
latent bug since the ring_mask inception in commit 73ae478cdf6a
("drm/i915: Replace has_bsd/blt/vebox with a mask").

To prevent similar mishaps in future, add a WARN_ON() if we find
ourselves with a device without any rings.

Fixes: 73ae478cdf6a ("drm/i915: Replace has_bsd/blt/vebox with a mask")
Fixes: 88d2ba2e95c8 ("drm/i915: Unify engine init loop")
Signed-off-by: Chris Wilson <[email protected]>
Cc: Tvrtko Ursulin <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Ben Widawsky <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]
Reviewed-by: Joonas Lahtinen <[email protected]>
Cc: [email protected]