soong: create phony package to fix dirty builds (2/2)

Add twrp_soong as a required module to ensure twres
folder is included in dirty builds where device out folder
is removed

Change-Id: I5b3f57664cd2aa97ff74ff594c72e6f29c6c927f
diff --git a/prebuilt/Android.mk b/prebuilt/Android.mk
index d409be0..ec2bb19 100755
--- a/prebuilt/Android.mk
+++ b/prebuilt/Android.mk
@@ -401,7 +401,7 @@
         LOCAL_POST_INSTALL_CMD += \
             && cp $(TARGET_OUT_ETC)/mke2fs.conf $(TARGET_RECOVERY_ROOT_OUT)/system/etc/mke2fs.conf
     endif
-LOCAL_REQUIRED_MODULES += init_second_stage.recovery reboot.recovery plat_service_contexts plat_hardware_contexts vndservice_contexts
+LOCAL_REQUIRED_MODULES += init_second_stage.recovery reboot.recovery plat_service_contexts plat_hardware_contexts vndservice_contexts twrp_soong
 include $(BUILD_PHONY_PACKAGE)
 
 # copy license file for OpenAES