default to device type of last build if no device type is given

platform_tools/android/bin/android_setup.sh

Index: platform_tools/android/bin/android_setup.sh
diff --git a/platform_tools/android/bin/android_setup.sh b/platform_tools/android/bin/android_setup.sh
index fc3b6699f9d888007ddc77afd697af1100b366a4..e18008e7544f2801764b2cd11765805ad50ced5c 100755
--- a/platform_tools/android/bin/android_setup.sh
+++ b/platform_tools/android/bin/android_setup.sh
@@ -160,9 +160,15 @@ setup_device() {
   # Setup the build variation depending on the target device
   TARGET_DEVICE="$1"
 
+
   if [ -z "$TARGET_DEVICE" ]; then
-    echo "INFO: no target device type was specified so using the default 'arm_v7'"
-    TARGET_DEVICE="arm_v7"
+    if [ -f .android_config ]; then
+      TARGET_DEVICE=$(cat .android_config)
+      echo "INFO: no target device was specified so using the device (${TARGET_DEVICE}) from the most recent build"
+    else
+      TARGET_DEVICE="arm_v7"  
+      echo "INFO: no target device type was specified so using the default '${TARGET_DEVICE}'"
+    fi
   fi
 
   case $TARGET_DEVICE in