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/common/css_pm.c b/plat/arm/css/common/css_pm.c
index 93d51fe..39c02af 100644
--- a/plat/arm/css/common/css_pm.c
+++ b/plat/arm/css/common/css_pm.c
@@ -300,4 +300,7 @@
 	.read_mem_protect	= arm_psci_read_mem_protect,
 	.write_mem_protect	= arm_nor_psci_write_mem_protect,
 #endif
+#if CSS_USE_SCMI_SDS_DRIVER
+	.system_reset2		= css_system_reset2,
+#endif
 };