ARM64: kernel: psci: let ACPI probe PSCI version

PSCI v0.2+ allows the kernel to probe the PSCI firmware version.

This patch replaces the default initialization of PSCI v0.2+
functions with code that allows probing PSCI firmware version
and initializes PSCI functions accordingly.

Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: NHanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/kernel/psci.c

@@ -439,9 +439,7 @@ int __init psci_acpi_init(void)
 	else
 		invoke_psci_fn = __invoke_psci_fn_smc;
 
-	psci_0_2_set_functions();
-
-	return 0;
+	return psci_probe();
 }
 
 #ifdef CONFIG_SMP