drm/i915: Add enum for hardware engine identifiers

Put the engine hardware id in the common header so they are
not only associated with the GuC since they are needed for
the legacy semaphores implementation.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -146,8 +146,14 @@ struct intel_engine_cs {
 #define I915_NUM_ENGINES 5
 #define _VCS(n) (VCS + (n))
 	unsigned int exec_id;
-	unsigned int hw_id;
-	unsigned int guc_id; /* XXX same as hw_id? */
+	enum intel_engine_hw_id {
+		RCS_HW = 0,
+		VCS_HW,
+		BCS_HW,
+		VECS_HW,
+		VCS2_HW
+	} hw_id;
+	enum intel_engine_hw_id guc_id; /* XXX same as hw_id? */
 	u64 fence_context;
 	u32		mmio_base;
 	unsigned int irq_shift;