Add Android.bp and auto-generated Rust code

The "use_addcarry" cfg is disabled as it's not supported on arm and
aarch64.

Bug: 193833713
Change-Id: If69ec41db93335f3514a490be9b4f816287600cb
diff --git a/cargo2android.json b/cargo2android.json
new file mode 100644
index 0000000..d59f27e
--- /dev/null
+++ b/cargo2android.json
@@ -0,0 +1,7 @@
+{
+  "cfg-blocklist": ["use_addcarry"],
+  "copy-out": true,
+  "device": true,
+  "run": true,
+  "tests": true
+}