Show Bitmap.Config value when unable to handle.

Part of investigating http://b/3201172.

Change-Id: I76a31c968b4c60beb079349a0722aa9a4ea5921c
diff --git a/graphics/java/android/renderscript/Allocation.java b/graphics/java/android/renderscript/Allocation.java
index 9dc291b..0de53f2 100644
--- a/graphics/java/android/renderscript/Allocation.java
+++ b/graphics/java/android/renderscript/Allocation.java
@@ -352,7 +352,7 @@
         if (bc == Bitmap.Config.RGB_565) {
             return Element.RGB_565(rs);
         }
-        throw new RSInvalidStateException("Bad bitmap type.");
+        throw new RSInvalidStateException("Bad bitmap type: " + bc);
     }
 
     static private Type typeFromBitmap(RenderScript rs, Bitmap b) {