merge from https://github.com/abbrev/fatfs.git
(cf1fa008119c8ae2d05311ba3d97da0c4dca33b6)
Signed-off-by: NCliff Chen <cliff.chen@rock-chips.com>
Change-Id: I321ba7933e1a4d6c07b3fbaa2a134eb54bb43b32

Add cconfig.h file for different version of GCC, which is automatically
detected and generated by scons script.

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;

1. Add poll/select APIs;
2. Add wait queue implementation;
3. Remove DFS_STATUS_* code and use errno;
4. Add pipe API;
5. Use a standalone fops in DFS;