[Kernel] Make comments in more accurate way

Update board.h

Update stm32f40x_flash.icf

Export the end address of ram, to avoid hard-code heap size in application

Use *.icf ram symbal, to avoid hardcode.

[DFS] 修正romfs在输入的目录名称比实际的名称短时存在的判断错误

比如实际目录为abcde，msh执行 cd abc也能执行成功，判断名称时存在bug

[BSP] Update and rename readme.txt to readme.md in stm32f4

[BSP] include iar startup code in stm32f4

[BSP] Create stm32f40x_flash.icf

fixed bug: 'scons --target=iar -s' output iar project missing startup code, and link file

修复scons生成IAR工程中没有startup code和链接文件，导致工程中断异常和Finsh无法工作

[bsp][stm32f746g-disco] Fix MPU init bug.

1. Fixed the bug that MPU init function was called 2 times.

[Finsh] Fix the mkfs command parameter issue.

Add C++ files support;
Fix the two same group issue if to add a library into an exist group.