goldfish: build stagefright cmd for testing purpose

It will be located in system_ext/bin, and handy
for testing audio/video files

adb push file.mp4 /data/local/tmp
adb shell
stagefright -S /data/local/tmp/file.mp4

Change-Id: I8216dc5fb19f468f2758823734c20ffdf67105e6
diff --git a/vendor.mk b/vendor.mk
index a56fb94..9391186 100644
--- a/vendor.mk
+++ b/vendor.mk
@@ -64,6 +64,7 @@
     audio.primary.goldfish \
     audio.primary.goldfish_legacy \
     power.goldfish \
+    stagefright \
     power.ranchu \
     fingerprint.ranchu \
     android.hardware.graphics.composer@2.1-impl \