Instead of using a "I kmalloced this" flag, we keep track of the kmalloced
strings and use that list to check if we need to kfree (in practice, the
list is very short).

This means that kparams can be const again, and plugs a leak.  This
is important for drivers/usb/gadget/nokia.c which gets modprobe/rmmod'ed
frequently on the N9000.
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>
Reviewed-by: NTakashi Iwai <tiwai@suse.de>
Cc: Artem Bityutskiy <dedekind1@gmail.com>
Tested-by: NPhil Carmody <ext-phil.2.carmody@nokia.com>