doc: Enable intersphinx

Allow referencing to Zephyr documentation with the intersphinx
extension.

Signed-off-by: Pieter De Gendt <[email protected]>

Author: pdgendt

doc/conf.py

@@ -13,6 +13,7 @@
     "sphinx_rtd_theme",
     "sphinx_tabs.tabs",
     'sphinx.ext.autodoc',
+    "sphinx.ext.intersphinx",
 ]
 
 templates_path = [str(WEST_BASE / 'doc' / '_templates')]
@@ -28,6 +29,10 @@
 html_logo = str(WEST_BASE / "doc" / "_static" / "images" / "logo.png")
 html_static_path = [str(WEST_BASE / 'doc' / '_static')]
 
+intersphinx_mapping = {
+    "zephyr": ("https://docs.zephyrproject.org/latest/", None),
+}
+
 pygments_style = "sphinx"
 highlight_language = "none"