Send m3_ctl i2c traffic over ice by default

The separate software bus idea wasn't the greatest, it still could
be used, but the better interface would be for all messages to go
over the ICE channel and the fake_ice unit could connect to the
software bus is appropriate.

Also fix a few small issues in the ice library related to i2c handling
Remove extraneous print
Update dma_test for mmio endianness

Tools print bytes sequentially, update the dma_test program to
send 'deadbeef' such that it prints sanely