xtensa: xtfpga: fix integer overflow in TASK_SIZE

This fixes the following warning when default memory region crosses
0x80000000:

  arch/xtensa/include/asm/processor.h:40:47: warning:
    integer overflow in expression [-Woverflow]
    #define TASK_SIZE (PLATFORM_DEFAULT_MEM_START + PLATFORM_DEFAULT_MEM_SIZE)
                                               ^
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/platforms/xtfpga/include/platform/hardware.h

@@ -12,13 +12,15 @@
  * This file contains the hardware configuration of the XTAVNET boards.
  */
 
+#include <asm/types.h>
+
 #ifndef __XTENSA_XTAVNET_HARDWARE_H
 #define __XTENSA_XTAVNET_HARDWARE_H
 
 /* Memory configuration. */
 
-#define PLATFORM_DEFAULT_MEM_START CONFIG_DEFAULT_MEM_START
-#define PLATFORM_DEFAULT_MEM_SIZE  CONFIG_DEFAULT_MEM_SIZE
+#define PLATFORM_DEFAULT_MEM_START __XTENSA_UL(CONFIG_DEFAULT_MEM_START)
+#define PLATFORM_DEFAULT_MEM_SIZE  __XTENSA_UL(CONFIG_DEFAULT_MEM_SIZE)
 
 /* Interrupt configuration. */