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/rpi/common/rpi3_pm.c b/plat/rpi/common/rpi3_pm.c
index 456e160..4dfe8f0 100644
--- a/plat/rpi/common/rpi3_pm.c
+++ b/plat/rpi/common/rpi3_pm.c
@@ -272,7 +272,7 @@
 	.pwr_domain_off = rpi3_pwr_domain_off,
 	.pwr_domain_on = rpi3_pwr_domain_on,
 	.pwr_domain_on_finish = rpi3_pwr_domain_on_finish,
-	.pwr_domain_pwr_down_wfi = rpi3_pwr_down_wfi,
+	.pwr_domain_pwr_down = rpi3_pwr_down_wfi,
 	.system_off = rpi3_system_off,
 	.system_reset = rpi3_system_reset,
 	.validate_power_state = rpi3_validate_power_state,