When allocating memory from bootmem for the kernel to use, try to leave about

2MB of memory in the bootmem allocator for the SDK to use internally at a later
point.  It'd be nice if there were some functions we could call before
allocating memory to let various facilities reserve some memory, but for now
this seems sufficient.  Previously some unfortunate systems could give up all
(or at least most) of their memory to the kernel from bootmem, and then
allocating command queues for packet output and the like would fail later in
the boot process (which in turn would lead to crashes even later.)

Reported by:	kan

sys/mips/cavium/octeon_machdep.c

@@ -287,6 +287,14 @@ octeon_memory_init(void)
 	 */
 	i = 0;
 	while (i < PHYS_AVAIL_ENTRIES) {
+		/*
+		 * If there is less than 2MB of memory available in 128-byte
+		 * blocks, do not steal any more memory.  We need to leave some
+		 * memory for the command queues to be allocated out of.
+		 */
+		if (cvmx_bootmem_available_mem(128) < 2 << 20)
+			break;
+
 		addr = cvmx_bootmem_phy_alloc(1 << 20, phys_end,
 					      ~(vm_paddr_t)0, PAGE_SIZE, 0);
 		if (addr == -1)