Refactor readback mux implementation. Improves performance (#155) and eliminates illegal streaming operator usage (#165)

src/peakrdl_regblock/readback/templates/readback_no_rt.sv

@@ -0,0 +1,17 @@
+always_comb begin
+    automatic logic [{{cpuif.data_width-1}}:0] readback_data_var;
+    readback_data_var = '0;
+    {{readback_mux|indent}}
+    readback_data = readback_data_var;
+
+    {%- if ds.has_external_addressable %}
+    readback_done = decoded_req & ~decoded_req_is_wr & ~decoded_req_is_external;
+    {%- else %}
+    readback_done = decoded_req & ~decoded_req_is_wr;
+    {%- endif %}
+    {%- if ds.err_if_bad_addr or ds.err_if_bad_rw %}
+    readback_err = decoded_err;
+    {%- else %}
+    readback_err = '0;
+    {%- endif %}
+end