m68knommu: clean up mm/init_no.c

The memory initialization code for m68knommu has grown a bit crufty,
clean it up.

. remove unused declaration for die_if_kernel()
. remove un-needed declaration of free_initmem()
. removed unused definitions of empty_bad_page and empty_bad_page_table
. removed unused DEBUG code
. make free_initmem() proper prototype

Signed-off-by: Greg Ungerer <gerg@uclinux.org>