NTB: Handle 64bit BAR sizes

commit 113fc505 upstream.

64bit BAR sizes are permissible with an NTB device.  To support them
various modifications and clean-ups were required, most significantly
using 2 32bit scratch pad registers for each BAR.

Also, modify the driver to allow more than 2 Memory Windows.

Signed-off-by: Jon Mason <jon.mason@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>