perf/arm_cspmu: Clean up ACPI dependency

Build-wise, the ACPI dependency consists of only a couple of things
which could probably stand being factored out into ACPI helpers anyway.
However for the immediate concern of working towards Devicetree support
here, it's easy enough to make a few tweaks to contain the affected code
locally, such that we can relax the Kconfig dependency.

Reviewed-and-Tested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Ilkka Koskinen <ilkka@os.amperecomputing.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/9d126711c7498b199b3e6f5cf48ca60ffb9df54c.1685983270.git.robin.murphy@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

drivers/perf/arm_cspmu/Kconfig

@@ -4,8 +4,7 @@
 
 config ARM_CORESIGHT_PMU_ARCH_SYSTEM_PMU
 	tristate "ARM Coresight Architecture PMU"
-	depends on ARM64 && ACPI
-	depends on ACPI_APMT || COMPILE_TEST
+	depends on ARM64 || COMPILE_TEST
 	help
 	  Provides support for performance monitoring unit (PMU) devices
 	  based on ARM CoreSight PMU architecture. Note that this PMU

drivers/perf/arm_cspmu/arm_cspmu.c

@@ -28,7 +28,6 @@
 #include <linux/module.h>
 #include <linux/perf_event.h>
 #include <linux/platform_device.h>
-#include <acpi/processor.h>
 
 #include "arm_cspmu.h"
 #include "nvidia_cspmu.h"
@@ -1075,6 +1074,9 @@ static int arm_cspmu_request_irq(struct arm_cspmu *cspmu)
 	return 0;
 }
 
+#if defined(CONFIG_ACPI) && defined(CONFIG_ARM64)
+#include <acpi/processor.h>
+
 static inline int arm_cspmu_find_cpu_container(int cpu, u32 container_uid)
 {
 	u32 acpi_uid;
@@ -1099,7 +1101,7 @@ static inline int arm_cspmu_find_cpu_container(int cpu, u32 container_uid)
 	return -ENODEV;
 }
 
-static int arm_cspmu_get_cpus(struct arm_cspmu *cspmu)
+static int arm_cspmu_acpi_get_cpus(struct arm_cspmu *cspmu)
 {
 	struct device *dev;
 	struct acpi_apmt_node *apmt_node;
@@ -1135,6 +1137,17 @@ static int arm_cspmu_get_cpus(struct arm_cspmu *cspmu)
 
 	return 0;
 }
+#else
+static int arm_cspmu_acpi_get_cpus(struct arm_cspmu *cspmu)
+{
+	return -ENODEV;
+}
+#endif
+
+static int arm_cspmu_get_cpus(struct arm_cspmu *cspmu)
+{
+	return arm_cspmu_acpi_get_cpus(cspmu);
+}
 
 static int arm_cspmu_register_pmu(struct arm_cspmu *cspmu)
 {