kmem.py: by default suppress display of zero-size objects

In particular, this causes mmio & copyregion objects to not be shown.

Change-Id: I8293ecd743e3be8cf72407e57491c09d3076e492

kmem-tool/kmem.py

diff --git a/kmem-tool/kmem.py b/kmem-tool/kmem.py
index e35abae..867e920 100644
--- a/kmem-tool/kmem.py
+++ b/kmem-tool/kmem.py
@@ -108,6 +108,9 @@
         # Copy Regions are immidately freed to create a hole in virtual memory
         total -= sizes[component_name].get(FrameType.COPYREGION, 0)
 
+        if total == 0 and not details:
+            continue
+
         grand_total += total
         print(
             pad_right(component_name, col_widths[0]) +