board/lm3s6965-ek: restore 128K kflash

This reverts both 2afdcfb and 0a0af89 to restore the 128K kflash
design as the implementation depends on that to work, checked with:

```
$ qemu-system-arm -M lm3s6965evb -nographic -device \
    loader,file=nuttx.bin,addr=0x0 -device \
    loader,file=nuttx_user.bin,addr=0x2000
```

Signed-off-by: Yanfeng Liu <yfliu2008@qq.com>

boards/arm/tiva/lm3s6965-ek/scripts/memory.ld

@@ -26,8 +26,8 @@ MEMORY
 {
     /* 256Kb FLASH */
 
-  kflash (rx)      : ORIGIN = 0x00000000, LENGTH = 124K
-  uflash (rx)      : ORIGIN = 0x0001f000, LENGTH = 132K
+  kflash (rx)      : ORIGIN = 0x00000000, LENGTH = 128K
+  uflash (rx)      : ORIGIN = 0x00020000, LENGTH = 128K
   xflash (rx)      : ORIGIN = 0x00040000, LENGTH = 0K
 
     /* 64Kb of contiguous SRAM */