Allow ARM Standard platforms to dynamically define PSCI capability

The capabilities exposed by the PSCI generic layer depends on the hooks
populated by the platform in `plat_arm_psci_pm_ops`. Currently ARM
Standard platforms statically define this structure. However, some
platforms may want to modify the hooks at runtime before registering
them with the generic layer.

This patch introduces a new ARM platform layer API
`plat_arm_psci_override_pm_ops` which allows the platform to probe
the power controller and modify `plat_arm_psci_pm_ops` if required.
Consequently, 'plat_arm_psci_pm_ops' is no longer qualified as
`const` on ARM Standard platforms.

Change-Id: I7dbb44b7bd36c20ec14ded5ee45a96816ca2ab9d
Signed-off-by: Soby Mathew <soby.mathew@arm.com>
diff --git a/include/plat/arm/common/plat_arm.h b/include/plat/arm/common/plat_arm.h
index 29fcffe..bc32e40 100644
--- a/include/plat/arm/common/plat_arm.h
+++ b/include/plat/arm/common/plat_arm.h
@@ -220,4 +220,7 @@
 unsigned int plat_arm_calc_core_pos(u_register_t mpidr);
 const mmap_region_t *plat_arm_get_mmap(void);
 
+/* Allow platform to override psci_pm_ops during runtime */
+const plat_psci_ops_t *plat_arm_psci_override_pm_ops(plat_psci_ops_t *ops);
+
 #endif /* __PLAT_ARM_H__ */