feat(psci): introduce 'pwr_domain_off_early' hook

This patch introduces the 'pwr_domain_off_early'  hook for
platforms wanting to perform housekeeping steps before the
PSCI framework starts the CPU power off sequence. Platforms
might also want to use ths opportunity to ensure that the
CPU off sequence can proceed.

The PSCI framework expects a return code of PSCI_E_DENIED,
if the platform wants to halt the CPU off sequence.

Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>
Change-Id: I6980e84fc4d6cb80537a178d0d3d26fb28a13853
diff --git a/include/lib/psci/psci.h b/include/lib/psci/psci.h
index 6d27b7b..4d7e58e 100644
--- a/include/lib/psci/psci.h
+++ b/include/lib/psci/psci.h
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2013-2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2023, NVIDIA Corporation. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -317,6 +318,7 @@
 	void (*cpu_standby)(plat_local_state_t cpu_state);
 	int (*pwr_domain_on)(u_register_t mpidr);
 	void (*pwr_domain_off)(const psci_power_state_t *target_state);
+	int (*pwr_domain_off_early)(const psci_power_state_t *target_state);
 	void (*pwr_domain_suspend_pwrdown_early)(
 				const psci_power_state_t *target_state);
 #if PSCI_OS_INIT_MODE