[tools,topgen] Enhance topgen

This is a big change in topgen. Some salient changes:
- It always regenerates from scratch the ipgen in-memory configurations
  (as IpBlock objects) so it is truly incremental: the previous flow
  reused the pre-existing generated ipgen hjson if found.
- It delays the actual ipgen file generation until the complete top config
  is generated. This is a step towards breaking topgen into smaller and
  mutually independent steps, thus enabling parallelizing them.
- On each pass it uses the most up-to-date top config, and detects
  convergence if the top configs from one pass and the previous one match.
- It converges with a single pass of process_top (though a second pass is
  done to enable the comparison).
- The generated RTL with and without these changes is identical.
In order to accomplish this some important changes are made:
- Call some of the merge_top functions suitable for each specific ipgen
  prior to generating the in-memory hjson config. This means not all
  IpBlock objects are available, so these merge functions are instrumented
  to skip missing blocks.
- The generation of ipgens are ordered according to dependencies. This
  order is created from the expected block functionality, so is not derived
  from a constructed graph, but converging in one pass means it is correct.
- Calling merge functions early means some of the objects in the in-memory
  top config are not plain dictionaries but are classes, so the code needs
  to handle either.

Part of lowRISC#25920

Signed-off-by: Guillermo Maturana <[email protected]>

hw/top_darjeeling/ip/xbar_dbg/data/autogen/xbar_dbg.gen.hjson

@@ -153,4 +153,69 @@
   ]
   clock: clk_dbg_i
   type: xbar
+  inter_signal_list:
+  [
+    {
+      name: tl_dbg
+      struct: tl
+      package: tlul_pkg
+      type: req_rsp
+      act: rsp
+      inst_name: dbg
+      width: 1
+      default: ""
+      external: true
+      top_signame: dbg_tl
+      conn_type: false
+      index: -1
+    }
+    {
+      name: tl_rv_dm__dbg
+      struct: tl
+      package: tlul_pkg
+      type: req_rsp
+      act: req
+      inst_name: dbg
+      width: 1
+      default: ""
+      top_signame: rv_dm_dbg_tl_d
+      index: -1
+    }
+    {
+      name: tl_mbx_jtag__soc
+      struct: tl
+      package: tlul_pkg
+      type: req_rsp
+      act: req
+      inst_name: dbg
+      width: 1
+      default: ""
+      top_signame: mbx_jtag_soc_tl_d
+      index: -1
+    }
+    {
+      name: tl_lc_ctrl__dmi
+      struct: tl
+      package: tlul_pkg
+      type: req_rsp
+      act: req
+      inst_name: dbg
+      width: 1
+      default: ""
+      top_signame: lc_ctrl_dmi_tl
+      index: -1
+    }
+    {
+      name: tl_soc_dbg_ctrl__jtag
+      struct: tl
+      package: tlul_pkg
+      type: req_rsp
+      act: req
+      inst_name: dbg
+      width: 1
+      default: ""
+      top_signame: soc_dbg_ctrl_jtag_tl
+      index: -1
+    }
+  ]
 }