drm/radeon: clarify and extend wb setup on APUs and NI+ asics

Use family rather than DCE check for clarity, also always use
wb on APUs, there will never be AGP variants.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_device.c

@@ -241,8 +241,8 @@ int radeon_wb_init(struct radeon_device *rdev)
 				rdev->wb.use_event = true;
 		}
 	}
-	/* always use writeback/events on NI */
-	if (ASIC_IS_DCE5(rdev)) {
+	/* always use writeback/events on NI, APUs */
+	if (rdev->family >= CHIP_PALM) {
 		rdev->wb.enabled = true;
 		rdev->wb.use_event = true;
 	}