fix(n1sdp): add platform-specific power domain functions

Commit 4d8c18196378824e388cf31ef991ba8fbbb09cbf added a redistributor
power off to resolve an error on N1SDP/Morello. Prior to this fix,
turning off both cores in a cluster would cause a hang when powering
back on either core. This change introduced issues on other platforms
with a different GIC implementation, and was reverted in commit
60719e4e0965aead49d927f12bf2a37bd2629012.

This commit uses the previous fix in platform-specific implementations
of power domain off/suspend functions.

Signed-off-by: Werner Lewis <werner.lewis@arm.com>
Change-Id: I52c463646c494fe931ff4ce47afb940a56978fcd
diff --git a/plat/arm/board/n1sdp/n1sdp_pm.c b/plat/arm/board/n1sdp/n1sdp_pm.c
new file mode 100644
index 0000000..e43832a
--- /dev/null
+++ b/plat/arm/board/n1sdp/n1sdp_pm.c
@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2023, Arm Limited. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <lib/psci/psci.h>
+#include <plat/arm/common/plat_arm.h>
+#include <plat/arm/css/common/css_pm.h>
+
+#include "n1sdp_private.h"
+
+/*******************************************************************************
+ * N1SDP specific functions called when turning off or suspending a power
+ * domain. Both additionally disable the GIC redistributor interface as cores
+ * are disabled to let cluster-PPU state transition to completion when a
+ * cluster is powered down.
+ ******************************************************************************/
+void n1sdp_pwr_domain_off(const psci_power_state_t *target_state)
+{
+	css_pwr_domain_off(target_state);
+	plat_arm_gic_redistif_off();
+}
+
+void n1sdp_pwr_domain_suspend(const psci_power_state_t *target_state)
+{
+	css_pwr_domain_suspend(target_state);
+	plat_arm_gic_redistif_off();
+}