Pull cmpswap implementation into archbcm2.c to avoid bringing in libc…

….a dependencies on lock

bcm/archbcm2.c

@@ -232,10 +232,24 @@ l2ap(int ap)
 	return (AP(0, (ap)));
 }
 
+int
+cas32(void* addr, u32int old, u32int new)
+{
+	int r, s;
+
+	s = splhi();
+	if(r = (*(u32int*)addr == old))
+		*(u32int*)addr = new;
+	splx(s);
+	if (r)
+		coherence();
+	return r;
+}
+
 int
 cmpswap(long *addr, long old, long new)
 {
-	return cas((ulong*)addr, old, new);
+	return cas32((ulong*)addr, old, new);
 }
 
 void