arm64: dts: armada-3720-turris-mox: Add missing interrupt for RTC

MCP7940MT-I/MNY RTC has connected interrupt line to GPIO2_5.

Fixes: 7109d817 ("arm64: dts: marvell: add DTS for Turris Mox")
Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>