Adds TTS voice packs in gs-common

TTS voice packs are better to be common for all devices
So the other device configs can have the common TTS voice packs
  for the device build  by "gs-common/device.mk"

And see doc, Preload Google Text-to-Speech (TTS) Voice Packs:
The voice packs are dowloanded follow the steps.

Bug: 140145973
Test: build passed and manual test
Change-Id: Ifed0ccecf598c1b09608b45494193524da3b9ed2
diff --git a/device.mk b/device.mk
index f686621..4787315 100644
--- a/device.mk
+++ b/device.mk
@@ -14,6 +14,8 @@
 # limitations under the License.
 #
 
+include device/google/gs-common/tts/voice_packs.mk
+
 PRODUCT_SOONG_NAMESPACES += \
 	device/google/gs-common/powerstats