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/plat/mediatek/lib/pm/mtk_pm.c b/plat/mediatek/lib/pm/mtk_pm.c
index 772c2d7..553fad2 100644
--- a/plat/mediatek/lib/pm/mtk_pm.c
+++ b/plat/mediatek/lib/pm/mtk_pm.c
@@ -45,8 +45,8 @@
 		mtk_pm_ops.get_sys_suspend_power_state = ops->get_sys_suspend_power_state;
 	}
 
-	if (!mtk_pm_ops.pwr_domain_pwr_down_wfi)
-		mtk_pm_ops.pwr_domain_pwr_down_wfi = ops->pwr_domain_pwr_down_wfi;
+	if (!mtk_pm_ops.pwr_domain_pwr_down)
+		mtk_pm_ops.pwr_domain_pwr_down = ops->pwr_domain_pwr_down_wfi;
 
 	mtk_pm_status |= MTK_PM_ST_PWR_READY;
 #endif