The read and write interfaces of a AXI bus are independent other than that
they use the same clock. Yet when connecting a single read-only and a
single write-only interface to a Xilinx AXI interconnect it instantiates
arbitration logic between the two interfaces. This is dead logic and
unnecessarily utilizes the FPGAs resources.
Introduce a new helper module that takes a read-only and a write-only AXI
interface and combines them into a single read-write interface. The only
restriction here is that all three interfaces need to use the same clock.
This module is useful for systems which feature a read DMA and a write DMA.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>