The picodvi PR #7880 switched the saved word to the watchdog
register since it reworked the RAM layout. This works for
reset_into_safe_mode because the watchdog scratch registers are
preserved by soft resets. They *aren't* preserved for pressing the
reset button. So it broken manual safe mode. Switch back to using
RAM to store the saved word but use the pico-sdks "uninitialized"
designation instead of a fixed location.
Also fixes USB host feather status neopixel by setting the power
pin.
Jeff Epler
Scott Shawcroft
Dan Halbert