ARM: dts: turris-omnia: describe switch interrupt

Describe switch interrupt for Turris Omnia so that the CPU does not have
to poll the switch. We also need to to set mpp45 pin to gpio function
for this.

Signed-off-by: Marek Behún <kabel@kernel.org>
Fixes: 26ca8b52 ("ARM: dts: add support for Turris Omnia")
Cc: linux-arm-kernel@lists.infradead.org
Cc: Uwe Kleine-König <uwe@kleine-koenig.org>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Gregory CLEMENT <gregory.clement@bootlin.com>
Cc: Andreas Färber <afaerber@suse.de>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>