dt: pmu: extend ARM PMU binding to allow for explicit interrupt affinity

The current ARM PMU binding relies on the PMU interrupts being listed in
CPU logical order, which the device-tree author simply cannot know
anything about.

This patch introduces a new "interrupt-affinity" property, which makes
the relationship between the PMU interrupts and their corresponding
CPU explicit.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

Documentation/devicetree/bindings/arm/pmu.txt

@@ -24,6 +24,13 @@ Required properties:
 
 Optional properties:
 
+- interrupt-affinity : Valid only when using SPIs, specifies a list of phandles
+                       to CPU nodes corresponding directly to the affinity of
+		       the SPIs listed in the interrupts property.
+
+		       This property should be present when there is more than
+		       a single SPI.
+
 - qcom,no-pc-write : Indicates that this PMU doesn't support the 0xc and 0xd
                      events.