scripts: dts: Output paths relative to $ZEPHYR_BASE

Requested by Marc Herbert. Makes the output deterministic as long as all
binding directories are within $ZEPHYR_BASE (and a bit less spammy too).

Example output for header:

Before:

    /*  Directories with bindings: /home/ulf/z/z/dts/bindings  */
    ...
    /*  Binding (...): /home/ulf/.../arm,v7m-nvic.yaml  */

After:

    /*  Directories with bindings: $ZEPHYR_BASE/dts/bindings  */
    ...
    /*  Binding (...): $ZEPHYR_BASE/dts/.../arm,v7m-nvic.yaml  */

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>

scripts/dts/gen_defines.py

@@ -19,6 +19,8 @@
 # edtlib. This will keep this script simple.
 
 import argparse
+import os
+import pathlib
 import sys
 
 import edtlib
@@ -40,7 +42,8 @@ def main():
 
     out_comment("Generated by gen_defines.py", blank_before=False)
     out_comment("DTS input file: " + args.dts, blank_before=False)
-    out_comment("Directories with bindings: " + ", ".join(args.bindings_dirs),
+    out_comment("Directories with bindings: " +
+                ", ".join(map(relativize, args.bindings_dirs)),
                 blank_before=False)
 
     active_compats = set()
@@ -54,7 +57,8 @@ def main():
 
             out_comment("Devicetree node: " + node.path)
             out_comment("Binding (compatible = {}): {}".format(
-                            node.matching_compat, node.binding_path),
+                            node.matching_compat,
+                            relativize(node.binding_path)),
                         blank_before=False)
             out_comment("Binding description: " + node.description,
                         blank_before=False)
@@ -111,6 +115,22 @@ def parse_args():
     return parser.parse_args()
 
 
+def relativize(path):
+    # If 'path' is within $ZEPHYR_BASE, returns it relative to $ZEPHYR_BASE,
+    # with a "$ZEPHYR_BASE/..." hint at the start of the string. Otherwise,
+    # returns 'path' unchanged.
+
+    zbase = os.getenv("ZEPHYR_BASE")
+    if zbase is None:
+        return path
+
+    try:
+        return str("$ZEPHYR_BASE" / pathlib.Path(path).relative_to(zbase))
+    except ValueError:
+        # Not within ZEPHYR_BASE
+        return path
+
+
 def write_regs(node):
     # Writes address/size output for the registers in the node's 'reg' property