perf: xgene: Add APM X-Gene SoC Performance Monitoring Unit driver

This patch adds a driver for the SoC-wide (AKA uncore) PMU hardware
found in APM X-Gene SoCs.

Signed-off-by: Tai Nguyen <ttnguyen@apm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>

drivers/perf/Kconfig

@@ -12,4 +12,11 @@ config ARM_PMU
 	  Say y if you want to use CPU performance monitors on ARM-based
 	  systems.
 
+config XGENE_PMU
+        depends on PERF_EVENTS && ARCH_XGENE
+        bool "APM X-Gene SoC PMU"
+        default n
+        help
+          Say y if you want to use APM X-Gene SoC performance monitors.
+
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