We're using the ACPI interface to detect whether we're dealing with a Thinkpad
or not. This way we're not loading the thinkpad_acpi module when we're not on
a Thinkpad, but at the same time, we give the opportunity to check for, and
potentially enable, both present and future Thinkpad with mute/micmute LEDs.

At least those running the ALC269 family (269 to 299) of Realtek codecs.

Cc: Alex Hung <alex.hung@canonical.com>
Tested-by: NHui Wang <hui.wang@canonical.com>
Signed-off-by: NDavid Henningsson <david.henningsson@canonical.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>