fix(plat/rcar3): change stack size of BL31

Increase the stack size to avoid stack overflow
when the LOG_LEVEL compile option is set high.

Signed-off-by: Hideyuki Nitta <hideyuki.nitta.jf@hitachi.com>
Signed-off-by: Toshiyuki Ogasahara <toshiyuki.ogasahara.bo@hitachi.com>
Signed-off-by: Yoshifumi Hosoya <yoshifumi.hosoya.wj@renesas.com>
Change-Id: I25047322763bff148dba13848a3a40f4c7cf90b7

plat/renesas/common/include/platform_def.h

@@ -40,7 +40,7 @@
 #define PLATFORM_STACK_SIZE	U(0x400)
 #endif
 #elif IMAGE_BL31
-#define PLATFORM_STACK_SIZE	U(0x400)
+#define PLATFORM_STACK_SIZE	U(0x800)
 #elif IMAGE_BL32
 #define PLATFORM_STACK_SIZE	U(0x440)
 #endif