The removal of this file appears to have been premature; it's not a feature enabled by Kconfig, but it's a arch-level feature regardless. Put it back for now until some happy future time when we decide how we really want to document such features. This reverts commit 2bef69a385b4c1c01d8abae0aa035f0ffa051f07. Signed-off-by: Jonathan Corbet <corbet@lwn.net>