Android.mk: make xtest installed in the vendor partition

and use ta libs in the vendor partition,
so that we could make optee work with Treble enabled builds too

Acked-by: Victor Chong <victor.chong@linaro.org>
Signed-off-by: Yongqin Liu <yongqin.liu@linaro.org>
diff --git a/host/xtest/regression_1000.c b/host/xtest/regression_1000.c
index 06773ef..3cbe90c 100644
--- a/host/xtest/regression_1000.c
+++ b/host/xtest/regression_1000.c
@@ -648,7 +648,7 @@
 #ifdef CFG_SECSTOR_TA_MGMT_PTA
 #ifndef TA_DIR
 # ifdef __ANDROID__
-#define TA_DIR "/system/lib/optee_armtz"
+#define TA_DIR "/vendor/lib/optee_armtz"
 # else
 #define TA_DIR "/lib/optee_armtz"
 # endif