Add axi_burst_unwrap

[niwis]

Add a module that converts wrapping bursts into up to two incremental bursts.

The first incremental burst covers the region from the start address to the wrap boundary. The second burst covers the region from the aligned base address to the start address. In the special case of an aligned start address, the wrapping burst can be trivially converted into a single incremental burst.

By splitting wrapping bursts that wrap around the wrap boundary into two incremental bursts, the ordering of the read/write transactions is preserved and no data buffering is required.

This module hasn't been properly verified yet.