dt-bindings: arm: Add Cortex-R52 to the list of enum

As a pre-requisite for porting Xen on a Cortex-R52 based System-on-chip, we
need to add "cortex-r52" to the list of enum.

Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@amd.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230518152730.82954-1-ayan.kumar.halder@amd.com


Signed-off-by: Rob Herring <robh@kernel.org>