[WIP] dts: gen_defines: emit dependency ordinal related macros

This really ought to be namespaced better, which kind of depends on
what we do after the rules are laid out following zephyrproject-rtos#22556.

Emit macros for each node's device tree dependency ordinal.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>

scripts/dts/gen_defines.py

@@ -60,6 +60,7 @@ def main():
             flash_area_num += 1
 
         if node.enabled and node.matching_compat:
+            write_deps(node)
             write_regs(node)
             write_irqs(node)
             write_props(node)
@@ -192,6 +193,12 @@ def relativize(path):
         return path
 
 
+def write_deps(node):
+    # Writes dependency ordinal information for the node.
+
+    out_node(node, 'DEP_ORDINAL', node.dep_ordinal)
+
+
 def write_regs(node):
     # Writes address/size output for the registers in the node's 'reg' property