fix(psci): add optional pwr_domain_validate_suspend to plat_psci_ops_t

This patch adds a new optional member `pwr_domain_validate_suspend` to
the `plat_psci_ops_t` structure that allows a platform to optionally
perform platform specific validations in OS-initiated mode. This is
conditionally compiled into the build depending on the value of the
`PSCI_OS_INIT_MODE` build option.

In https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/17682,
the return type of the `pwr_domain_suspend` handler was updated from
`void` to `int` to allow a platform to optionally perform platform
specific validations in OS-initiated mode. However, when an error code
other than `PSCI_E_SUCCESS` is returned, the current exit path does not
undo the operations in `psci_suspend_to_pwrdown_start`, and as a result,
the system ends up in an unexpected state.

The fix in this patch prevents the need to undo the operations in
`psci_suspend_to_pwrdown_start`, by allowing the platform to first
perform any necessary platform specific validations before the PSCI
generic code proceeds to the point of no return where the CPU_SUSPEND
request is expected to complete successfully.

Change-Id: I05d92c7ea3f5364da09af630d44d78252185db20
Signed-off-by: Wing Li <wingers@google.com>
diff --git a/lib/psci/psci_private.h b/lib/psci/psci_private.h
index b9987fe..04f93bd 100644
--- a/lib/psci/psci_private.h
+++ b/lib/psci/psci_private.h
@@ -298,6 +298,8 @@
 #endif
 void psci_get_target_local_pwr_states(unsigned int end_pwrlvl,
 				      psci_power_state_t *target_state);
+void psci_set_target_local_pwr_states(unsigned int end_pwrlvl,
+				      const psci_power_state_t *target_state);
 int psci_validate_entry_point(entry_point_info_t *ep,
 			uintptr_t entrypoint, u_register_t context_id);
 void psci_get_parent_pwr_domain_nodes(unsigned int cpu_idx,