Move registration into android package

Mutator registration is tightly coupled with the android package, move
all registration from the soong package to the android package.

Test: build.ninja identical
Change-Id: Ie183d0b52cc7431c9e05b231934d189208ef1efe
diff --git a/cc/ndk_sysroot.go b/cc/ndk_sysroot.go
index 144d91c..cbdaa26 100644
--- a/cc/ndk_sysroot.go
+++ b/cc/ndk_sysroot.go
@@ -55,14 +55,13 @@
 import (
 	"github.com/google/blueprint"
 
-	"android/soong"
 	"android/soong/android"
 )
 
 func init() {
-	soong.RegisterModuleType("ndk_headers", ndkHeadersFactory)
-	soong.RegisterModuleType("ndk_library", ndkLibraryFactory)
-	soong.RegisterSingletonType("ndk", NdkSingleton)
+	android.RegisterModuleType("ndk_headers", ndkHeadersFactory)
+	android.RegisterModuleType("ndk_library", ndkLibraryFactory)
+	android.RegisterSingletonType("ndk", NdkSingleton)
 
 	pctx.Import("android/soong/common")
 }