USB: UHCI: Add support for big endian mmio

This patch adds support for big endian mmio to the UHCI HCD. Big endian
mmio is supported by adding a flag bit to the UHCI HCD replicating the
solution used in the EHCI HCD.

When adding big endian support this patch also adds a check to see if we
need to support HCs with PCI I/O registers when we support HCs with MMIO.

This patch also adds 'const' to the register access functions' uhci_hcd
argument.

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>