[POWERPC] macintosh/windfarm: Fix platform driver hotplug/coldplug

Since 43cc71eed1250755986da4c0f9898f9a635cb3bf, the platform modalias
is prefixed with "platform:".  Add MODULE_ALIAS() to the hotpluggable
"macintosh" platform drivers, to re-enable auto loading.

[dbrownell@users.sourceforge.net: registration fixes]
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>