init: mount tracefs before apexd-bootstrap

This removes the error log when apexd-bootstrap starts:

  cutils-trace: Error opening trace file: No such file or directory (2)

Bug: 376150518
Test: boot-time trace shows apexd-bootstrap
  see https://source.android.com/docs/core/perf/boot-times#systrace
Change-Id: I5feaece50663a602b61377cee034060fd30217f9