PSCI: Fix MISRA defects in common and setup code

MISRA C-2012 Rules 10.1, 10.3, 17.8 and 20.7.

Change-Id: I3980bd2a1d845559af4bbe2887a0250d0506a064
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/include/lib/psci/psci.h b/include/lib/psci/psci.h
index f2ee62e..71d605d 100644
--- a/include/lib/psci/psci.h
+++ b/include/lib/psci/psci.h
@@ -344,7 +344,7 @@
 		       unsigned int lowest_affinity_level);
 int psci_migrate(u_register_t target_cpu);
 int psci_migrate_info_type(void);
-long psci_migrate_info_up_cpu(void);
+u_register_t psci_migrate_info_up_cpu(void);
 int psci_node_hw_state(u_register_t target_cpu,
 		       unsigned int power_level);
 int psci_features(unsigned int psci_fid);