ARM64: dts: marvell: armada-37xx: Fix GIC maintenance interrupt

The GIC-500 integrated in the Armada-37xx SoCs is compliant with
the GICv3 architecture, and thus provides a maintenance interrupt
that is required for hypervisors to function correctly.

With the interrupt provided in the DT, KVM now works as it should.
Tested on an Espressobin system.

Fixes: adbc3695

 ("arm64: dts: add the Marvell Armada 3700 family and
a development board")
Cc: <stable@vger.kernel.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>