drm/i915: Add SW_SYNC to our recommend testing Kconfig

Since we do use the SW_SYNC in igt for validating dma-fence and
sync_file, and wish to expand usage to cover driver independent portions
of syncobj interaction, ensure SW_SYNC is included in our testing
Kconfig.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jason Ekstrand <jason.ekstrand@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170810094036.4307-1-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/Kconfig.debug

@@ -25,6 +25,7 @@ config DRM_I915_DEBUG
         select DRM_VGEM # used by igt/prime_vgem (dmabuf interop checks)
         select DRM_DEBUG_MM if DRM=y
 	select DRM_DEBUG_MM_SELFTEST
+	select SW_SYNC # signaling validation framework (igt/syncobj*)
 	select DRM_I915_SW_FENCE_DEBUG_OBJECTS
 	select DRM_I915_SELFTEST
         default n