Test Realtime implementation

[danielinux]

• Try to figure out worst-case scenario response time for a RT task
• Ensure that the deadline time is constant if a task is marked as RT

[brabo]

Setting up basic latency testing on F4 and F7 discos.

[danielinux]

Worst case scenario: Constant 23 μs latency with 5 busyloop in background. Tested with latency tool.