drm/i915: Move engine IDs out of i915_reg.h

drm/i915: Move engine IDs out of i915_reg.h

To remove the dependency between the GT headers and i915_reg.h, move the
definition of the engine IDs/classes to intel_engine_types.h

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190816012343.36433-3-daniele.ceraolospurio@intel.com