drm/i915: Include i915_scheduler.h from i915_gem_context.h

struct i915_gem_context embeds struct i915_sched_attr so needs to include
the respective header.
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180524150621.17332-1-tvrtko.ursulin@linux.intel.com

drivers/gpu/drm/i915/i915_gem_context.h

@@ -30,6 +30,7 @@
 #include <linux/radix-tree.h>
 
 #include "i915_gem.h"
+#include "i915_scheduler.h"
 
 struct pid;