chore(docs): drop the "wfi" from `pwr_domain_pwr_down_wfi`

To allow for generic handling of a wakeup, this hook is no longer
expected to call wfi itself. Update the name everywhere to reflect this
expectation so that future platform implementers don't get misled.

Change-Id: Ic33f0b6da74592ad6778fd802c2f0b85223af614
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
diff --git a/lib/psci/psci_off.c b/lib/psci/psci_off.c
index dbc646c..577fdd7 100644
--- a/lib/psci/psci_off.c
+++ b/lib/psci/psci_off.c
@@ -163,9 +163,9 @@
 		    RT_INSTR_ENTER_HW_LOW_PWR,
 		    PMF_NO_CACHE_MAINT);
 #endif
-		if (psci_plat_pm_ops->pwr_domain_pwr_down_wfi != NULL) {
+		if (psci_plat_pm_ops->pwr_domain_pwr_down != NULL) {
 			/* This function may not return */
-			psci_plat_pm_ops->pwr_domain_pwr_down_wfi(&state_info);
+			psci_plat_pm_ops->pwr_domain_pwr_down(&state_info);
 		}
 
 		psci_pwrdown_cpu_end_terminal();