checks: Add interrupt provider test

An interrupt provider (an actual interrupt-controller node or an
interrupt nexus) should have both #address-cells and #interrupt-cells
properties explicitly defined.

Add an extra test for this. We check for the #interrupt-cells property
already, but this does not cover every controller so far, only those that
get referenced by an interrupts property in some node. Also we miss
interrupt nexus nodes.

A missing #address-cells property is less critical, but creates
ambiguities when used in interrupt-map properties, so warn about this as
well now.
This removes the now redundant warning in the existing interrupts test.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20200515141827.27957-2-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

tests/bad-interrupt-controller.dts

@@ -0,0 +1,7 @@
+/dts-v1/;
+
+/ {
+	intc: interrupt-controller {
+		interrupt-controller;
+	};
+};