[BSP] [ASM9260T] Fix compile errors.

1. Add Heap_Size define for Keil toolchain
2. Disable pthreads in rtconfig.h

bsp/asm9260t/platform/rt_low_level_keil.inc

@@ -29,4 +29,5 @@ ABT_STK_SIZE EQU 512
 IRQ_STK_SIZE EQU 1024
 FIQ_STK_SIZE EQU 1024
 SYS_STK_SIZE EQU 512
+Heap_Size    EQU 512
     END

bsp/asm9260t/rtconfig.h

@@ -65,7 +65,7 @@
 /* SECTION: the runtime libc library */
 /* the runtime libc library */
 #define RT_USING_LIBC
-#define RT_USING_PTHREADS
+//#define RT_USING_PTHREADS
 
 /* Using Module System */
 //#define RT_USING_MODULE