Remap Eee PC touchpad toggle key to F21 used by X

Remap Eee PC touchpad toggle key to F21 used by X

Currently, Eee PC have a hotkey that generates KEY_F13 but this
will soon change to KEY_TOUCHPAD_TOOGLE.  Both cases do not
work well with X.

X has defined F21 for the purpose of touchpad toggle and other
udev keymaps align with this meaning.  Patch aligns Eee PC
hotkey drivers with F21.

Tested on Eee PC 1005PE using both eeepc-wmi and eeepc-laptop driver
(with acpi_osi="!Windows 2009").

Signed-off-by: Chris Bagwell <chris@cnpbagwell.com>
Signed-off-by: Martin Pitt <martin.pitt@ubuntu.com>