1. Move struct stat to libc_stat.h;
2. Defined a new FD_SET macros in libc_fdset.h.

update SConscript: support scons 3.

[bsp] update i.mx rt 1052 bsp

[BSP] update bsp/stm32f429-apollo/KConfig

[Examples] update examples/network

[BSP] update stm32f429-apollo .config rtconfig.h

[BSP] Fix the linkup state for ETH initialization.

[BSP] Repalce RT_LWIP_IPADDR RT_LWIP_GWADDR RT_LWIP_MSKADDR define

[bsp]Fix RT_LWIP_IPADDR RT_LWIP_GWADDR RT_LWIP_MSKADDR define, replace multi-bytes MACRO with single string MACRO.

[bsp] add i.mx rt 1052 support

Use RT_LWIP_IPADDR/GWADDR/MSKADDR to replace old options:
RT_LWIP_GWADDR0/1/2/3 etc.

[lwIP] update lwipdhcpd scons groupname

[BSP] Fix the align issue in __bss_start. 
[Tools] Auto-detect the parameter type in SrcRemove.

[BSP] 增加龙芯1c的硬件SPI相关接口

[DFS] Fix `fd_new` failed return value.