DMM Python examples cannot be run as `redpitaya` user

[abdomit]

This concerns the DMM Python example provided here: https://github.com/RedPitaya/RedPitaya-Examples/tree/dev/API_examples/Python_API/DMM

According to my tests these examples requires root privileges. It does not work as redpitaya user, although this user is a member of the dma group which makes believe that it should be able to use AXI DMA.

It is probably also true for the C++ example, but I haven't tried.

[b-swat]

The API for memory access uses /dev/mem (https://github.com/RedPitaya/RedPitaya/blob/master/rp-api/api/src/axi_manager.cpp#L99), and this device requires root privileges.
I'm aware of this security issue. However, I haven't yet created separate devices for the reserved memory block without direct access to /dev/mem. We might improve this by release 3.1. But for now, there is no time for it.