docs: kernel_include.py: add sphinx build dependencies

The files included by kernel-include should be added as build
dependencies, in order for sphinx-build to rebuild the corresponding
docs if any changes at the included file happens.

Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Link: https://lore.kernel.org/r/d30fc4fa422a13b7e1623d690945c46b58a55e79.1648290305.git.mchehab@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/sphinx/kernel_include.py

@@ -59,6 +59,7 @@ class KernelInclude(Include):
     u"""KernelInclude (``kernel-include``) directive"""
 
     def run(self):
+        env = self.state.document.settings.env
         path = os.path.realpath(
             os.path.expandvars(self.arguments[0]))
 
@@ -70,6 +71,8 @@ class KernelInclude(Include):
 
         self.arguments[0] = path
 
+        env.note_dependency(os.path.abspath(path))
+
         #return super(KernelInclude, self).run() # won't work, see HINTs in _run()
         return self._run()