USB: UHCI: Support big endian GRUSBHC HC

This patch adds support for big endian GRUSBHC UHCI controllers.
The HCD bus glue will probe the register interface to determine
the endianness of the controller.

Tested on GR-LEON4-ITX board which has a controller with little endian
interface and on custom LEON3 board with a BE controller.

Signed-off-by: Jan Andersson <jan@gaisler.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>