msi-laptop: send out touchpad on/off key

MSI BIOS's raw behavior is send out KEY_TOUCHPAD_TOGGLE key when user
pressed touchpad hotkey.

Actually, we can capture the real touchpad status by read 0xE4 EC address
on MSI netbook/notebook. So, add msi-laptop input device for send out
KEY_TOUCHPAD_ON or KEY_TOUCHPAD_OFF key when user pressed Fn+F3 touchpad
hotkey. It leave userland applications to know the real touchpad status.

Tested on MSI netbook U-100, U-115, U160(N051), U160DX, N014, N034
Tested on MSI notebook CR620

Cc: Carlos Corbacho <carlos@strangeworlds.co.uk>
Cc: Matthew Garrett <mjg@redhat.com>
Cc: Dmitry Torokhov <dtor@mail.ru>
Cc: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Lee, Chun-Yi <jlee@novell.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>