use legacy DRM playback for legacy widevine content

Bug: 18006370
Change-Id: If949e57303be958eba20629700b1b35e76c70afe
diff --git a/device-common.mk b/device-common.mk
index 8c33d69..681d9e3 100644
--- a/device-common.mk
+++ b/device-common.mk
@@ -28,6 +28,7 @@
     wifi.interface=wlan0 \
     wifi.supplicant_scan_interval=15 \
     tf.enable=y \
+    persist.sys.media.legacy-drm=true \
     drm.service.enabled=true
 
 # libhwui flags