Enable lowmemory trace events in atrace

Enable collection of lowmemory events in atrace as a category. These
events have been available in the kernel, but not exposed via atrace.

Bug: https://github.com/catapult-project/catapult/issues/3557
Test: Run "atrace memreclaim", trigger LMK events.
Change-Id: I92140518796bdda8b302d566d7d78e2129b9839c