usb/isp1760: Move to native-endian ptds

This helps users with platform-bus-connected isp176xs, big-endian cpu,
and missing byteswapping on the data bus. It does so by collecting all
SW byteswaps in one place and also fixes a bug with non-32-bit io
transfers on this hardware, where payload has to be byteswapped
instead of ptds.

Signed-off-by: Arvid Brodin <arvid.brodin@enea.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>