[POWERPC] Fix breakage caused by 72486f1f

72486f1f inverted the sense for enabling
hotplug CPU controls without reference to any other architecture other than
i386, ia64 and PowerPC.  This left everyone else without hotplug CPU control.

Fix powerpc for this brain damage.

(akpm: patch adapted from rmk's ARM fix.  Changelog stolen from rmk)

Signed-off-by: Giuliano Pochini <pochini@shiny.it>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>