Input: allocate keycode for Fn + right shift

Input: allocate keycode for Fn + right shift

The last 2 generations of Lenovo Thinkpads send an acpi_thinkpad event when
Fn + right shift is pressed.  This is intended for use with "Lenovo Quick
Clean" software, which disables the touchpad + kbd for 2 minutes on this
key-combo so that healthcare workes can disinfect it.

But there is no silkscreen print on the right-keyboard to indicate this,
so add a KEY_FN_RIGHT_SHIFT keycode define to use for this key-combo.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20200908135147.4044-3-hdegoede@redhat.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>