qemu/qemu_sbsa: increase size to handle fdt

64KB was not enouth to handle fdt, bl2 shows
following error message.

"ERROR:   Invalid Device Tree at 0x10000000000: error -3"

This patch increases the size to 1MB to address above error.
Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Change-Id: I0726a0cea95087175451da0dba7410acd27df808

plat/qemu/qemu_sbsa/include/platform_def.h

@@ -233,7 +233,7 @@
  * DT related constants
  */
 #define PLAT_QEMU_DT_BASE		NS_DRAM0_BASE
-#define PLAT_QEMU_DT_MAX_SIZE		0x10000
+#define PLAT_QEMU_DT_MAX_SIZE		0x100000
 
 /*
  * System counter