svn revisions r269964 and r269963 seemed to have impaired small memory

footprint systems(32M/64M) and didn't leave enough free memory to load modules
when it was setting up page tables that for sizes that are never used on
these smallish boards.

Set kmem_zmax to PAGE_SIZE on these smaller systems (< 128M) to keep this
from happening. Verified on mips32 h/w.

PR:             193465
Submitted by:   delphij
Reviewed by:    adrian

sys/kern/kern_malloc.c

@@ -717,6 +717,8 @@ kmeminit(void)
 	 * a given architecture.
 	 */
 	mem_size = vm_cnt.v_page_count;
+	if (mem_size <= 32768) /* delphij XXX 128MB */
+		kmem_zmax = PAGE_SIZE;
 
 	if (vm_kmem_size_scale < 1)
 		vm_kmem_size_scale = VM_KMEM_SIZE_SCALE;