Introduce ARM platform APIs for GICv3 Redistributor

As with other ARM platform GIC APIs, these directly invoke the GICv3
driver APIs for Redistributor power management.

For the sake of uniform GIC API, empty stubs are placed for those GIC
drivers that lack Redistributor component.

Change-Id: Iad0d760d4dbca790998f7768cda621ff3b15a864
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>
diff --git a/include/plat/arm/common/plat_arm.h b/include/plat/arm/common/plat_arm.h
index bc32e40..c167aa2 100644
--- a/include/plat/arm/common/plat_arm.h
+++ b/include/plat/arm/common/plat_arm.h
@@ -194,6 +194,8 @@
 void plat_arm_gic_init(void);
 void plat_arm_gic_cpuif_enable(void);
 void plat_arm_gic_cpuif_disable(void);
+void plat_arm_gic_redistif_on(void);
+void plat_arm_gic_redistif_off(void);
 void plat_arm_gic_pcpu_init(void);
 void plat_arm_security_setup(void);
 void plat_arm_pwrc_setup(void);