Move namespace mutator earlier to support defaults

The prebuilts and defaults mutators start adding some dependencies, so
for them to be able to reference imported modules, we need to
run the namespace mutator earlier.

Test: m nothing
Test: Try to use a global defaults module from a namespace
Change-Id: I6e853d20e32251d0fd33c8b2dcc26c0695b808fd
diff --git a/android/mutator.go b/android/mutator.go
index 2f13f6c..64d9fdd 100644
--- a/android/mutator.go
+++ b/android/mutator.go
@@ -76,6 +76,7 @@
 	func(ctx RegisterMutatorsContext) {
 		ctx.TopDown("load_hooks", loadHookMutator).Parallel()
 	},
+	RegisterNamespaceMutator,
 	RegisterPrebuiltsPreArchMutators,
 	RegisterDefaultsPreArchMutators,
 }
@@ -86,7 +87,6 @@
 }
 
 var preDeps = []RegisterMutatorFunc{
-	RegisterNamespaceMutator,
 	registerArchMutator,
 }