ARM: dts: n900: remove mmc1 card detect gpio

Instead, expose the key via the input framework, as SW_MACHINE_COVER

The chip-detect GPIO is actually detecting if the cover is closed.
Technically it's possible to use the SD card with open cover. The
only downside is risk of battery falling out and user being able
to physically remove the card.

The behaviour of SD card not being available when the device is
open is unexpected and creates more problems than it solves. There
is a high chance, that more people accidentally break their rootfs
by opening the case without physically removing the card.

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/20200612125402.18393-3-merlijn@wizzup.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>