1. Change the type of cmd to 'int';
2. Remove RT_LWIP_USING_RT_MEM macro;

STM32F4系列UART在初始化的时候，如果GPIO_AF放到GPIO_INIT后边，系统复位后，串口会向外发送一个字节的数据，通常是0x00。将GPIO_AF放到GPIO_INIT前边可以避开这个问题。

[BSP] Fix component initialization functions may be not sequential storage on ROM when used for IAR linker.

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

Use *.icf ram symbal, to avoid hardcode.

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

[bugfix] Open the #define RT_USING_LWIP in rtconfig.h , then build it , the stm32_eth.h can not find.
Signed-off-by: pangwei <271372443@qq.com>

According to STM32 Manual, the USART RXNE flag will be clear automatically after
read to the USART_DR register[1], so the call to USART_ClearITPendingBit is
unnecessary.

[1]: See RM0090 Reference Manual p.992, Bit 5