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/toolchain_library.go b/cc/toolchain_library.go
index 0548da9..0097ca3 100644
--- a/cc/toolchain_library.go
+++ b/cc/toolchain_library.go
@@ -18,7 +18,6 @@
 	"github.com/google/blueprint"
 	"github.com/google/blueprint/proptools"
 
-	"android/soong"
 	"android/soong/android"
 )
 
@@ -27,7 +26,7 @@
 //
 
 func init() {
-	soong.RegisterModuleType("toolchain_library", toolchainLibraryFactory)
+	android.RegisterModuleType("toolchain_library", toolchainLibraryFactory)
 }
 
 type toolchainLibraryDecorator struct {