atrace.rc: keep tracepoint directories world readable/executable.

With kernel patch "tracefs: Have tracefs directories not set OTH
permission bits by default", sub directories in tracefs are changed
from mode 0755 to 0750 by default. This makes these directories only
accessible by root.

To make tracepoint directories accessbile from non-root users, this CL
sets them explicitly to mode 0755.

Bug: 208712503
Test: build and test manually
Change-Id: I8ab581b5fd69f4245f1a0169c0dcbe3c9646fc91