axi: Add AXI to AXI lite adapter module and testbench

Signed-off-by: Alex Forencich <alex@alexforencich.com>

README.md

@@ -26,6 +26,7 @@ To facilitate the dual-license model, contributions to the project can only be a
 
 *  AXI
     *  SV interface for AXI
+    *  AXI to AXI lite adapter
     *  Register slice
     *  Width converter
     *  Single-port RAM