Add systrace support
Created by: derkling
This series integrate the support for SysTrace which is now provided by TRAPpy. It adds also a board definition for a Nexus 5X device, which is not properly identified as a big.LITTLE system by devlib because of the old format used for "/proc/cpuinfo" in its default kernel. Being a standard device we can however easily defined the devlib::Platform to be used when this target is in use.
NOTE: this series depends on trappy HEAD being advanced to include: https://github.com/ARM-software/trappy/pull/162