xhci: dbc: don't use generic xhci ring allocation functions for dbc.

xhci: dbc: don't use generic xhci ring allocation functions for dbc.

The generic xhci ring allocations code needs struct xhci_hcd pointer, and
it allocates memory for the rings from dma pools created for the xhci
device.

In order to decouple xhci and DbC we have to create our own ring allocation
and free routines for DbC

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20200723144530.9992-20-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>