Add /sys/kernel/tracing/trace_marker to whitelist

Add /sys/kernel/tracing/trace_marker to whitelist of paths
that the zygote is allowed to keep open. It currently contains
/sys/kernel/debug/tracing/trace_marker which is only created when
debugfs is mounted. tracefs will be mounted at /sys/kernel/tracing
when debugfs is not mounted.

Test: AtraceHostTest
Bug: 148436518
Change-Id: I734120e8c88ba9d5451a1bd1589e084323824285