platform/x86: peaq-wmi: Add new peaq-wmi driver

PEAQ is a new European OEM, I've bought one of their 2-in-1 x86 devices,
which is actually quite a nice device. Under Windows it has Dolby
software for "better" sound and you can select different equalizer
presets using a special button.

This WMI interface for this button is not really nice, as it does not do
notifies (it really does not I triple checked), but since I had already
figured out the entire WMI interface for this I decided to go the full
mile anyway and implement a WMI based input driver for this using
input_polldev since, well, we need to poll.

This commit adds support for this button making it report KEY_SOUND
input events. KEY_SOUND is already used in various places to switch
sound into theatre mode and things like that so it seems appropriate
here.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
[dvhart: minor declaration ordering and commit log typo fixes]
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>