USB: isp1760: Support board-specific hardware configurations

This adds support for hardware configurations that don't match the
chip default register settings (e.g., 16-bit data bus, DACK and
DREQ pulled up instead of down, analog overcurrent mode).

These settings are passed in via the OF device tree.  The PCI
interface still assumes the same default values.

Signed-off-by: Nate Case <ncase@xes-inc.com>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>