Add DefaultsModule interface

Changes the InitDefaultsModule method from taking a DefaultableModule
to taking a DefaultsModule in preparation for adding visibility support
to defaults modules.

Bug: 130796911
Test: m nothing
Change-Id: I1d459da1017ae7f2654e7eb275cb424e52d85730
diff --git a/android/defaults.go b/android/defaults.go
index d1d3b18..9db0c36 100644
--- a/android/defaults.go
+++ b/android/defaults.go
@@ -107,6 +107,11 @@
 	return true
 }
 
+type DefaultsModule interface {
+	Module
+	Defaults
+}
+
 func (d *DefaultsModuleBase) properties() []interface{} {
 	return d.defaultableProperties
 }
@@ -114,7 +119,7 @@
 func (d *DefaultsModuleBase) GenerateAndroidBuildActions(ctx ModuleContext) {
 }
 
-func InitDefaultsModule(module DefaultableModule) {
+func InitDefaultsModule(module DefaultsModule) {
 	module.AddProperties(
 		&hostAndDeviceProperties{},
 		&commonProperties{},