ARMv8: Add basic PSCI framework

This patch introduces a generic ARMv8 PSCI framework, with all functions
returning a dummy ARM_PSCI_RET_NI (Not Implemented), then it is up to each
platform to implement their own functions based on this framework.

Signed-off-by: Hongbo Zhang <hongbo.zhang@nxp.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: York Sun <york.sun@nxp.com>
diff --git a/arch/arm/cpu/armv8/Kconfig b/arch/arm/cpu/armv8/Kconfig
index edae43d..22dce88 100644
--- a/arch/arm/cpu/armv8/Kconfig
+++ b/arch/arm/cpu/armv8/Kconfig
@@ -58,6 +58,16 @@
 	  It is no problem to set a larger value than the number of CPUs in
 	  the actual hardware implementation.
 
+config ARMV8_PSCI_CPUS_PER_CLUSTER
+	int "Number of CPUs per cluster"
+	depends on ARMV8_PSCI
+	default 0
+	help
+	  The number of CPUs per cluster, suppose each cluster has same number
+	  of CPU cores, platforms with asymmetric clusters don't apply here.
+	  A value 0 or no definition of it works for single cluster system.
+	  System with multi-cluster should difine their own exact value.
+
 if SYS_HAS_ARMV8_SECURE_BASE
 
 config ARMV8_SECURE_BASE