Convert Android.mk's to Soong.

A new Soong plugin is introduced to track cert files and generate
prebuilt_etc rules for each of them.

Bug: 122332220
Test: Manual build + comparison

Change-Id: I67c1d9c4240a3574975db8f82ff1a01b3e25178e
diff --git a/soong/Android.bp b/soong/Android.bp
new file mode 100644
index 0000000..252d314
--- /dev/null
+++ b/soong/Android.bp
@@ -0,0 +1,12 @@
+bootstrap_go_package {
+    name: "soong-ca-certificates",
+    pkgPath: "android/soong/system/ca-certificates",
+    deps: [
+        "soong-android",
+        "soong-phony",
+    ],
+    srcs: [
+        "ca_certificates.go",
+    ],
+    pluginFor: ["soong_build"],
+}