[efi] Leave asynchronous USB endpoints open until device is removed

[efi] Leave asynchronous USB endpoints open until device is removed

Some UEFI device drivers will react to an asynchronous USB transfer
failure by dubiously terminating the scheduled transfer from within
the completion handler.

We already have code from commit fbb776f ("[efi] Leave USB endpoint
descriptors in existence until device is removed") that avoids freeing
memory in this situation, in order to avoid use-after-free bugs.  This
is not sufficient to avoid potential problems, since with an xHCI
controller the act of closing the endpoint requires issuing a command
and awaiting completion via the event ring, which may in turn dispatch
further USB transfer completion events.

Avoid these problems by leaving the USB endpoint open (but with the
refill timer stopped) until the device is finally removed, as is
already done for control and bulk transfers.

Signed-off-by: Michael Brown <mcb30@ipxe.org>