dt: Add -machine dumpdtb option to dump the current dtb

Now that we are dynamically creating the dtb, it's really useful to
be able to dump the created blob for debugging.

This patch implements a -machine dumpdtb=<file> option for e500 that
dumps the dtb exactly in the form the guest would get it to disk. It
can then be analyzed by dtc to get information about the guest
configuration.

Signed-off-by: Alexander Graf <agraf@suse.de>

qemu-config.c

@@ -583,6 +583,10 @@ static QemuOptsList qemu_machine_opts = {
             .name = "dtb",
             .type = QEMU_OPT_STRING,
             .help = "Linux kernel device tree file",
+        }, {
+            .name = "dumpdtb",
+            .type = QEMU_OPT_STRING,
+            .help = "Dump current dtb to a file and quit",
         },
         { /* End of list */ }
     },