Input: add `SW_MACHINE_COVER`

This event code represents the state of a removable cover of a device.
Value 0 means that the cover is open or removed, value 1 means that the
cover is closed.

Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Merlijn Wajer <merlijn@wizzup.org>
Link: https://lore.kernel.org/r/20200612125402.18393-2-merlijn@wizzup.org


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>