Verify platform/architecture on updates
Verify platform/architecture on updates

This makes it more difficult to accidentally update a Raspberry Pi 0
with firmware for a different board. An easy mistake is to
accidentally set `MIX_TARGET=rpi` instead of `rpi0` and then lose the
USB gadget mode support on the update. With this change, that update
will fail.

nerves-project/nerves_system_rpi0,nerves-project/nerves_system_rpi0