ehci: diagnostics + hardening for the port-not-enabled case

Second OptiPlex QR: the Host System Error is gone (the 64-bit QH/qTD layout
fix worked), but the SETUP qTD now halts with TBYTES=0, C_ERR=3 and no
XactErr/Babble/DBE -- a split transaction with no valid response.  PORTSC
shows CCS=1, PP=1 but PED=0, i.e. the port never enabled, so the split has no
TT to address.  On Intel PCH a healthy USB2 port shows the rate-matching hub
as high-speed (PED=1), so the next step is to see every port's state.

- settle 100 ms after powering ports and clear stale change bits before the
  reset walk (RMHs come up slower than direct devices)
- retry the port reset once after settling
- log a clear line when a connected port remains disabled
- retry a failed full-speed device as low-speed (the PORTSC speed field is
  only valid once the port is enabled)
- persistent bottom-row summary: controller count, caps64, USB legacy handoff
  result, every connected port's PORTSC and the HID device count.  A hardware
  run without serial now reports the whole picture instead of one QR.

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