Fix for oops on rmmod caused by *_remove() function marked as __devinit
(and thus discarded after module initialization - if CONFIG_MODULES=y
and CONFIG_HOTPLUG is not set).
This patch changes __devinit to __devexit and adds __devexit_p() where
pointer to such function is used.

The only exception is au1000, where au1000_remove() is called from
cleanup_au1000() function - __devinit is jest removed there.