kselftest: devices: Move discoverable devices test to subdirectory

Move the discoverable devices test to a subdirectory to allow other
related tests to be added to the devices directory.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20240705-dev-err-log-selftest-v2-1-163b9cd7b3c1@collabora.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>