reset2: Add css_system_reset2()

This function implements the platform dependant part of PSCI system
reset2 for CSS platforms using SCMI.

Change-Id: I724389decab484043cadf577aeed96b349c1466d
Signed-off-by: Roberto Vargas <roberto.vargas@arm.com>
diff --git a/plat/arm/css/drivers/scp/css_scp.h b/plat/arm/css/drivers/scp/css_scp.h
index 4a6d473..1f0cf8e 100644
--- a/plat/arm/css/drivers/scp/css_scp.h
+++ b/plat/arm/css/drivers/scp/css_scp.h
@@ -15,6 +15,7 @@
 struct psci_power_state;
 
 /* API for power management by SCP */
+int css_system_reset2(int is_vendor, int reset_type, u_register_t cookie);
 void css_scp_suspend(const struct psci_power_state *target_state);
 void css_scp_off(const struct psci_power_state *target_state);
 void css_scp_on(u_register_t mpidr);