dt-bindings: interrupt-controller: arm,gic-v3: Make the v2 compat requirements explicit

A common mistake when writing a device tree for a platform that is using
GICv3 with ancient CPUs is to overlook the MMIO frames that implement
the GICv2 compatibility feature, because this feature is implemented by
the CPUs and not by the GIC itself.

The compatibility feature itself is optional (all the modern
implementations have dropped it), but is present in all the ARM Ltd
implementations of the ARMv8.0 architecture (A3x, A53, A57, A72, A73),
and many others from various implementers.

Make it explicit that GICC, GICH and GICV are required for these CPUs.
Also take this opportunity to update my email address, as people keep
sending them to the wrong place...
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Krzysztof Kozlowski <krzk+dt@kernel.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220409101617.268796-1-maz@kernel.org

Documentation/devicetree/bindings/interrupt-controller/arm,gic-v3.yaml

@@ -7,7 +7,7 @@ $schema: http://devicetree.org/meta-schemas/core.yaml#
 title: ARM Generic Interrupt Controller, version 3
 
 maintainers:
-  - Marc Zyngier <marc.zyngier@arm.com>
+  - Marc Zyngier <maz@kernel.org>
 
 description: |
   AArch64 SMP cores are often associated with a GICv3, providing Private
@@ -78,7 +78,11 @@ properties:
       - GIC Hypervisor interface (GICH)
       - GIC Virtual CPU interface (GICV)
 
-      GICC, GICH and GICV are optional.
+      GICC, GICH and GICV are optional, but must be described if the CPUs
+      support them. Examples of such CPUs are ARM's implementations of the
+      ARMv8.0 architecture such as Cortex-A32, A34, A35, A53, A57, A72 and
+      A73 (this list is not exhaustive).
+
     minItems: 2
     maxItems: 4096   # Should be enough?