Initial support for bitfurystrikesback m-board v2

I've added m-board bank selection code to this fork. I think it should work with your i2c slot selection too, but could not test it.

One thing to note is that it changes spi speed from 2mhz to 400khz. With 2mhz I can only detect about 20 chips per bank. Feel free to set it back, if necessary.

It also adds a new command line parameter --bitfury-board-type which defaults to i2c board, but can be setted to my m-board too.

Please pull if you find it worthwhile.

Thanks.