Add linkfiles needed for soong

Link build/soong/root.bp to $TOP/Android.bp and
build/soong/bootstrap.bash to $TOP/bootstrap.bash.
Change-Id: Icb77a068ce2bc37aec8ac97f1b4f20ae11c9573e

default.xml

@@ -13,7 +13,10 @@
   </project>
   <project path="build/blueprint" name="platform/build/blueprint" groups="pdk,tradefed" />
   <project path="build/kati" name="platform/build/kati" groups="pdk,tradefed" />
-  <project path="build/soong" name="platform/build/soong" groups="pdk,tradefed" />
+  <project path="build/soong" name="platform/build/soong" groups="pdk,tradefed" >
+    <linkfile src="root.bp" dest="Android.bp" />
+    <linkfile src="bootstrap.bash" dest="bootstrap.bash" />
+  </project>
   <project path="abi/cpp" name="platform/abi/cpp" groups="pdk" />
   <project path="art" name="platform/art" groups="pdk" />
   <project path="bionic" name="platform/bionic" groups="pdk" />