ARM: 8029/1: mcpm: Rename the power_down_finish() functions to be less confusing

The name "power_down_finish" seems to be causing some confusion,
because it suggests that this function is responsible for taking
some action to cause the specified CPU to complete its power down.

This patch renames the affected functions to "wait_for_powerdown"
and similar, since this function's intended purpose is just to wait
for the hardware to finish a powerdown initiated by a previous
cpu_power_down.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>