[MTD] [NAND] fix platform driver hotplug/coldplug

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

NOTE: at91_nand for some reason disallows modular builds.  I'm assuming that's
just an oversight that will be fixed.

[dbrownell@users.sourceforge.net: minor fix]
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>