arm64: Fix definition of arm_pm_restart to match the declaration

Commit ff701306 (arm64: use common reboot infrastructure) converted the
arm_pm_restart declaration to the new reboot infrastructure but missed
the actual definition.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/process.c

@@ -81,7 +81,7 @@ void soft_restart(unsigned long addr)
 void (*pm_power_off)(void);
 EXPORT_SYMBOL_GPL(pm_power_off);
 
-void (*arm_pm_restart)(char str, const char *cmd);
+void (*arm_pm_restart)(enum reboot_mode reboot_mode, const char *cmd);
 EXPORT_SYMBOL_GPL(arm_pm_restart);
 
 void arch_cpu_idle_prepare(void)