Circuit Python supports saving a single word of data across reboots.
Previously, this data was placed immediately following the .bss.
However, this appeared to not work, as Circuit Python zeroes out the
heap when it starts up, and the heap begins immediately after the .bss.
Switch to using the new .uninitialized section in order to store this
word across resets.
Signed-off-by: Sean Cross <sean@xobs.io>
3b5f5ddaa6