NTB: MFV 113fc505: Handle 64bit BAR sizes

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.

Authored by: Jon Mason
Obtained from: Linux
Sponsored by: EMC / Isilon Storage Division