drm/i915: Move the scheduler feature bits into the purview of the engines

Rather than having the high level ioctl interface guess the underlying
implementation details, having the implementation declare what
capabilities it exports. We define an intel_driver_caps, similar to the
intel_device_info, which instead of trying to describe the HW gives
details on what the driver itself supports. This is then populated by
the engine backend for the new scheduler capability field for use
elsewhere.

v2: Use caps.scheduler for validating CONTEXT_PARAM_SET_PRIORITY (Mika)
    One less assumption of engine[RCS] \o/

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tomasz Lis <tomasz.lis@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Tomasz Lis <tomasz.lis@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180207210544.26351-2-chris@chris-wilson.co.uk
Reviewed-by: Michel Thierry <michel.thierry@intel.com>
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index c1b80cd..32883bb 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3229,8 +3229,11 @@ void i915_gem_set_wedged(struct drm_i915_private *i915)
 		 * start to complete all requests.
 		 */
 		engine->submit_request = nop_complete_submit_request;
+		engine->schedule = NULL;
 	}
 
+	i915->caps.scheduler = 0;
+
 	/*
 	 * Make sure no request can slip through without getting completed by
 	 * either this call here to intel_engine_init_global_seqno, or the one