Change default arch for banchan to arm64

Devices that only support 32-bit are very uncommon. Default
to the arch that module authors are most likely to be using.

Test: banchan com.android.sdkext | grep TARGET_PRODUCT
Test: banchan com.android.sdkext arm | grep TARGET_PRODUCT
Test: banchan com.android.sdkext arm64 | grep TARGET_PRODUCT
Change-Id: I31734660318eabbe3279214980b5cdecb55ab80b

envsetup.sh

@@ -878,7 +878,7 @@ function banchan()
     fi
 
     if [ -z "$product" ]; then
-        product=arm
+        product=arm64
     elif [ $(echo $product | wc -w) -gt 1 ]; then
         echo "banchan: Error: Multiple build archs or products supplied: $products"
         return