Proposed changes to support pi4 and others

[s-k-tttttttt]

I've made these changes in order to get the tutorial to correctly run on a pi-4. The changes use the bcc_host library which provides an api call to resolve the peripheral base address for all models of pi, including the pi-4. I have tested on a pi-4, but not other models. Can you please test on your pi-3. I suspect if it works fine for you too, it will also be resolved for other pi models.

[fandahao17]

Cool! I'll try to get a Pi 3 this week and test this code. :)