This allows you to initialize usb_host.Port once successfully and
then returns the same object as long as you pass the same arguments
in. It does allow you to fix incorrect pins but not switching from
one valid set to another. (It needs a reset for that.)
This also moves hcd cache operations to RAM so that they don't
access the cache when doing maintenance.
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