platform/x86: lenovo-wmi-helpers: Add helper for creating per-device debugfs dir

platform/x86: lenovo-wmi-helpers: Add helper for creating per-device debugfs dir

We are about to add debugfs support for lenovo-wmi-capdata. Let's setup
a debugfs directory called "lenovo_wmi" for tidiness, so that any
lenovo-wmi-* device can put its subdirectory under the directory.
Subdirectories will be named after the corresponding WMI devices.

Signed-off-by: Rong Zhang <i@rong.moe>
Signed-off-by: Derek J. Clark <derekjohn.clark@gmail.com>
Link: https://patch.msgid.link/20260520060740.119554-7-derekjohn.clark@gmail.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>