asus-laptop: Add key found on Asus F3M

Asus F3M has two keys labeled with an icon of a touchpad. The first,
reported as 0x6B is next to the power key and the second, reported as
0x6A, is F9 combined with Fn button. When I was pressing the latter, I was
getting "Unknown key 6a pressed" message before applying this patch.

Asus F3M does not support WMI so the commit does not update key mappings
in the asus-nb-wmi.c file.

I have not tested this mapping on any other Asus laptop.

Signed-off-by: Łukasz Stelmach <stlman@poczta.fm>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>