rp2040, HIL: detach on warm restart and reset hub TT after cancelled splits (#4056)

- rp2040: dcd_init holds the pull-up off 2 ms when a warm restart left it
  attached; board_init resets USBCTRL when native USB is unused.
- test/hil: send Reset_TT to the DUT's multi-TT hub port before each flash
  and after usbtest unlink or failed cases; Linux xHCI never clears a TT
  buffer on URB cancel.
8 files changed