Merge #741

741: using arm-gic to programm the ARM Generic Interrupt Controller r=stlankes a=stlankes

- add timer support
- using the counter-timer physical count register to determine a timestamp
- using rusty_demo to test the aarch64 port
- solves #738 

Co-authored-by: Stefan Lankes <slankes@eonerc.rwth-aachen.de>