Signed-off-by: chenyong <1521761801@qq.com>

[components]add rt_device_ops for adc device and fix finsh_getchar() return wrong value in Big-endian status.

The serial getchar will only modify the LSB of ch, the MSB 3 bytes
will be unchanged as the random value on stack, so if MSB 3 bytes
not zero, the value got is wrong.

finsh_getchar invokes getchar, who's return type is int, and return value may < 0, which means error occurred or EOF.
finsh should handle that situation properly, and inform user about the error.

[finsh] add FINSH_ECHO_DISABLE_DEFAULT and remove FINSH_ECHO_MODE_DEFAULT, to control the finsh default echo mode

1. Add macro check in rtdebug.h;
2. Use RT_USING_POSIX for poll/select, stdin etc.
3. Split dfs_posix.h to dfs_posix.h, dfs_poll.h and dfs_select.h;

Use uint8_t/uint32_t etc to replace u_char/u_long etc;
Use getchar for shell input.