drivers/power: fix platform driver hotplug/coldplug

Since 43cc71ee ("platform: prefix MODALIAS
with "platform:"), the platform modalias is prefixed with "platform:".
Add MODULE_ALIAS() to the hotpluggable "power" drivers drivers, to
re-enable auto loading.

[dbrownell@users.sourceforge.net: one was missing]
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Greg KH <greg@kroah.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>