MFC r253404:
   o TxD ring requires 8 bytes alignment to work so change alignment
     constraint to 8. Previously it may have triggered watchdog
     timeouts.
   o Check whether interrupt is ours or not.
   o Enable interrupts before attemping to transmit queued packets.
     This will slightly improve TX performance.
   o No need to clear IFF_DRV_OACTIVE in a loop. AE_FLAG_TXAVAIL is
     used to know whether there are enough available TxD ring space.
   o Added missing bus_dmamap_sync(9) in ae_rx_intr() and rearranged
     code to avoid unncessary register access.
   o Make sure to clear TxD, TxS, RxD rings in driver initialization.
     Otherwise some data in these rings could be interpreted as
     'updated' which in turn will advance internally maintained
     pointers and can trigger watchdog timeouts.

  PR:	kern/180382
  Approved by:	re (hrs)
MFC r253532:

Fix an XHCI regression:

The Block Event Interrupts, BEI, feature does not
work like expected with the Renesas XHCI chipsets.
Revert feature.

While at it correct the TD SIZE computation in
case of Zero Length Packet, ZLP, in the end of a
multi frame USB transfer.

PR:             usb/180726
Approved by:    re, hrs