Added phony module type for soong.

The "required" field within "phony" module in .bp file has to be
non-empty. And "phony" module doesn't contain any "src" files.
Bug: b/32981153
Test: make -j out/soong/build.ninja

Change-Id: Iaa2009467c44702572b97ca9cbd02c1d368c8d83

android/androidmk.go

@@ -43,7 +43,7 @@ type AndroidMkData struct {
 	OutputFile OptionalPath
 	Disabled   bool
 
-	Custom func(w io.Writer, name, prefix string) error
+	Custom func(w io.Writer, name, prefix, moduleDir string) error
 
 	Extra []func(w io.Writer, outputFile Path) error
 }
@@ -185,7 +185,7 @@ func translateAndroidMkModule(ctx blueprint.SingletonContext, w io.Writer, mod b
 			prefix = "2ND_" + prefix
 		}
 
-		return data.Custom(w, name, prefix)
+		return data.Custom(w, name, prefix, filepath.Dir(ctx.BlueprintFile(mod)))
 	}
 
 	if data.Disabled {