malloc: use km_alloc(9) for kmemusage

[Martin Pieuchot]

Diff below convert a use of uvm_km_zalloc(9) to km_alloc(9), this memory
is never released, ok?

Index: kern/kern_malloc.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_malloc.c,v
retrieving revision 1.144
diff -u -p -r1.144 kern_malloc.c
--- kern/kern_malloc.c  23 Feb 2021 13:50:16 -0000      1.144
+++ kern/kern_malloc.c  22 Mar 2021 10:23:42 -0000
@@ -580,8 +580,8 @@ kmeminit(void)
            FALSE, &kmem_map_store);
        kmembase = (char *)base;
        kmemlimit = (char *)limit;
-       kmemusage = (struct kmemusage *) uvm_km_zalloc(kernel_map,
-               (vsize_t)(nkmempages * sizeof(struct kmemusage)));
+       kmemusage = km_alloc(round_page(nkmempages * sizeof(struct kmemusage)),
+           &kv_any, &kp_zero, &kd_waitok);
        for (indx = 0; indx < MINBUCKET + 16; indx++) {
                XSIMPLEQ_INIT(&bucket[indx].kb_freelist);
        }