perf/arm_cspmu: Add devicetree support

Hook up devicetree probing support. For now let's hope that people
implement PMIIDR properly and we don't need an override property or
match data mechanism.

Reviewed-by: Ilkka Koskinen <ilkka@os.amperecomputing.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Besar Wicaksono <bwicaksono@nvidia.com>
Tested-by: Besar Wicaksono <bwicaksono@nvidia.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/836722034302ff62f2df56aaeb0036e71945a5d1.1706718007.git.robin.murphy@arm.com
Signed-off-by: Will Deacon <will@kernel.org>