NXP-MCUBootUtility v2.3.1 release note

Improvements:

1. Can recognize source bootable image if FDCB doesn't start from offset 0
   可以支持FDCB位置不在偏移0地址的Bootable Image作为源文件
2. [RTyyyy] Do some blank check if erase unit is always 64KB in flashloader
   [RTyyyy] 在使用Flashloader里擦除操作时，某些情况下需要先检查目标区域是否为空

Bugfixes:

1. Read or Erase does sometimes not use correct parameters
   当连接得到的flash Page/Sector/Block Size信息有误时，无法做进一步下载
2. Setting spi speed option for 1bit SPI NOR device doesn't take effect
   设置恢复启动设备(1bit SPI NOR)的速度选项不生效
3. [RTyyyy] Cannot edit fuse cfg0 for RT1011 in friendly way
   [RTyyyy] 在RT1011下，无法确认fuse cfg0区域的可视化设置