drm/i915: introduce intel_ring_buffer structure (V2)

Introduces a more complete intel_ring_buffer structure with callbacks
for setup and management of a particular ringbuffer, and converts the
render ring buffer consumers to use it.

Signed-off-by: Zou Nan hai <nanhai.zou@intel.com>
Signed-off-by: Xiang Hai hao <haihao.xiang@intel.com>
[anholt: Fixed up whitespace fail and rebased against prep patches]
Signed-off-by: Eric Anholt <eric@anholt.net>

include/drm/i915_drm.h

@@ -616,7 +616,9 @@ struct drm_i915_gem_execbuffer2 {
 	__u32 num_cliprects;
 	/** This is a struct drm_clip_rect *cliprects */
 	__u64 cliprects_ptr;
-	__u64 flags; /* currently unused */
+#define I915_EXEC_RENDER                 (1<<0)
+#define I915_EXEC_BSD                    (1<<1)
+	__u64 flags;
 	__u64 rsvd1;
 	__u64 rsvd2;
 };