libcutils must check /sys/kernel/tracing for tracefs first

Currently it falls back to /sys/kernel/tracing if debugfs is not found.
/sys/kernel/tracing must be checked first since debugfs is not allowed
to be mounted in user builds starting with Android R launching devices.

Test: manual
Change-Id: I2fb5ec91bbf7d5304a1a6efcb06530969485e78f