platform/x86: wmi: add WMI support to MODULE_DEVICE_TABLE()

The kernel provides the macro MODULE_DEVICE_TABLE() where driver authors
can specify their device type and their array of device_ids and thereby
trigger the generation of the appropriate MODULE_ALIAS() output. This is
opposed to having to specify one MODULE_ALIAS() for each device. The WMI
device type is currently not supported.

While using MODULE_DEVICE_TABLE() does increase the complexity as well
as spreading out the implementation across the kernel, it does come with
some benefits too;
* It makes different drivers look more similar; if you can specify the
  array of device_ids any device type specific input to MODULE_ALIAS()
  will automatically be generated for you.
* It helps each driver avoid keeping multiple versions of the same
  information in sync. That is, both the array of device_ids and the
  potential multitude of MODULE_ALIAS()'s.

Add WMI support to MODULE_DEVICE_TABLE() by adding info about struct
wmi_device_id in devicetable-offsets.c and add a WMI entry point in
file2alias.c.

The type argument for MODULE_DEVICE_TABLE(type, name) is wmi.

Suggested-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Mattias Jacobsson <2pi@mok.nu>
Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>