DocBook: include !Emm/util.c in kernel-api to include, kzfree and more

Add the exported symbols from mm/util.c to the kernel-api memory
management section, to pick up obvious routines like kzfree and
krealloc.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Acked-by: Rob Landley <rob@landley.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>