Add ion/ion_stat to the atrace memory category

ion_stat was added to 4.19+ kernels as a successor to the existing
ion_heap_grow / shrink tracepoints

Bug: 154302786
Test: cuttlefish with new kernel, run atrace memory and cat /sys/kernel/tracing/events/ion/ion_stat/enable
Change-Id: I2502d281be0a1de5a0bde41482e70ad8ef29fd0b
diff --git a/cmds/atrace/atrace.cpp b/cmds/atrace/atrace.cpp
index 8637a31..28fdaa4 100644
--- a/cmds/atrace/atrace.cpp
+++ b/cmds/atrace/atrace.cpp
@@ -237,6 +237,7 @@
         { OPT,      "events/kmem/rss_stat/enable" },
         { OPT,      "events/kmem/ion_heap_grow/enable" },
         { OPT,      "events/kmem/ion_heap_shrink/enable" },
+        { OPT,      "events/ion/ion_stat/enable" },
     } },
 };