spapr: increase temporary fdt buffer size

At the moment the size of the buffer is set to 64K which is
enough for approximately 150 VCPUs which is not the limit.

This increases the buffer up to 256K which allows having
a tree for approximately 600 VCPUs which is way beyond the real
number we need.

As only the real size of the tree is copied to the guest, there
will be no impact on existing configurations.
Signed-off-by: NAlexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: NAlexander Graf <agraf@suse.de>

hw/ppc/spapr.c

@@ -62,7 +62,7 @@
  *
  * We load our kernel at 4M, leaving space for SLOF initial image
  */
-#define FDT_MAX_SIZE            0x10000
+#define FDT_MAX_SIZE            0x40000
 #define RTAS_MAX_SIZE           0x10000
 #define FW_MAX_SIZE             0x400000
 #define FW_FILE_NAME            "slof.bin"