spapr: Provide better error message when slots exceed max allowed

Currently when user specifies more slots than allowed max of
SPAPR_MAX_RAM_SLOTS (32), we error out like this:

qemu-system-ppc64: unsupported amount of memory slots: 64

Let the user know about the max allowed slots like this:

qemu-system-ppc64: Specified number of memory slots 64 exceeds max supported 32
Signed-off-by: NBharata B Rao <bharata@linux.vnet.ibm.com>
Reviewed-by: NDavid Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>

hw/ppc/spapr.c

@@ -1774,8 +1774,8 @@ static void ppc_spapr_init(MachineState *machine)
         ram_addr_t hotplug_mem_size = machine->maxram_size - machine->ram_size;
 
         if (machine->ram_slots > SPAPR_MAX_RAM_SLOTS) {
-            error_report("unsupported amount of memory slots: %"PRIu64,
-                          machine->ram_slots);
+            error_report("Specified number of memory slots %"PRIu64" exceeds max supported %d\n",
+                         machine->ram_slots, SPAPR_MAX_RAM_SLOTS);
             exit(EXIT_FAILURE);
         }