dt-bindings: arm: spe-pmu: convert to DT schema

Convert the Arm Statisical Profiling Extension (SPE) binding to DT
schema.
Not much to see here, basically just the announcement that SPE is
integrated on the system level and where the IRQ is routed to.

Move it into the more suitable perf/ directory on the way.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220506140533.3566431-3-andre.przywara@arm.com