Make tuning variable non-volatile

[DeepashriM]

For tuning.py, I am able to set the parameters in the command prompt (E.g: python tuning.py GAMMAVAD_SR 20).

But when ReSpeaker reboots (after power ON OFF cycle), parameter value changes to default (GAMMAVAD_SR: 15.0).

How can we set the parameter non-volatile (does not change).