dell: add new dell WMI format for the AIO machines

dell: add new dell WMI format for the AIO machines

There is a new DELL WMI spec. with new WMI event format.
I'm working on the AIO machines, but I think the new format will apply to
all the Dell's machines, not only for AIO, which will be released later
this year.

The new format of the WMI buffer is shown as below
word 0 - the number of words following in the WMI buffer(not including
        this word.
word 1 - the event type
	0x0000 - A hot key is pressed or an event occurred
	0x000F - A sequence of hot keys are pressed
word 2 and on - the event data

Signed-off-by: AceLan Kao <acelan.kao@canonical.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>