USB: Add support for Xilinx USB host controller

Add bus glue driver for Xilinx USB host controller. The controller can be
configured as HS only or HS/FS hybrid. The driver uses the device tree file
to configure the driver according to the setting in the hardware system.

This driver has been tested with usbtest using the NET2280 PCI card.

Signed-off-by: Julie Zhu <julie.zhu@xilinx.com>
Signed-off-by: John Linn <john.linn@xilinx.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>