Make sure powerdebug builds when we build systemimage

Signed-off-by: Vishal Bhoj <vishal.bhoj@hackbox.linaro.org>
diff --git a/Android.mk b/Android.mk
index 36c73cd..1bd60fb 100644
--- a/Android.mk
+++ b/Android.mk
@@ -9,6 +9,8 @@
 
 LOCAL_MODULE := powerdebug
 
+systemimage: powerdebug
+
 LOCAL_CPPFLAGS += \
 		-DDISABLE_I18N \
 		-DDISABLE_TRYCATCH \