hwdb: Add quirk to fix mapping of VIOS LTH17 touchpad toggle key

The touchpad toggle key (Fn + F6) on the VIOS LTH17 sends CTRL + META + F24
without this quirk. With this quirk it sends CTRL + META + F21, with F21
mapping to XF86TouchpadToggle, which is what we want.

Note that the CTRL + META modifiers being send together with the F21 are
still somewhat unusual, userspace will need to be thought to deal with
this as there is nothing we can do about this at the hwdb level. Note at
least one other laptop also sends CTRL + META + F21 instead of just F21.