axi_demux: Remove W select FIFO, add counter and register

CHANGELOG.md

@@ -323,6 +323,11 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - `axi_test::rand_axi_lite_slave` and `axi_test::rand_axi_lite_master`: Change type of address and
   data width parameters (`AW` and `DW`) from `int` to `int unsigned`.  Same rationale as for
   `AXI_BUS` (et al.) above.
+- `axi_demux`: Remove FIFO between AW and W channel, is now a register plus counter.
+               Prevents AWs to be emmitted downstream to a different master port as long as Ws
+               are still in flight to another. This prevents deadlock, if there is stalling
+               downstream.
+
 
 ### Fixed
 - `axi_demux`: Break combinatorial simulation loop.

src/axi_demux.sv

@@ -817,7 +817,6 @@ module axi_demux_intf #(
   parameter int unsigned MAX_TRANS        = 32'd8,
   parameter int unsigned AXI_LOOK_BITS    = 32'd3,
   parameter bit          UNIQUE_IDS       = 1'b0,
-  parameter bit          FALL_THROUGH     = 1'b0,
   parameter bit          SPILL_AW         = 1'b1,
   parameter bit          SPILL_W          = 1'b0,
   parameter bit          SPILL_B          = 1'b0,