amazon-thor: Switched to armv7

I have this device and thought I'd try an armhf install and then go on to switching to armv7 build as requested in: #599

Fresh installs of both the armhf and armv7 builds seem to get to the exact same stage during boot (blank screen after the PostmarketOS logo then loops back to bootloader) however, I did need to do a small config change for it to build successfully under armv7.

There are a couple of old issues/comments that indicate there are a few changes that could be made for this device. That's where I am going to explore them next and see if we can get this device back up and running again. :)

This is my first MR to PostmarketOS... If there is something I have missed or something that requires changes, please let me know and I'll try and fix it ASAP.