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

fatfs: mkfs时增加FM_SFD参数，减少文件系统对flash空间的占用

1. Remove INIT_FS_EXPORT and change INIT_DEVICE_EXPORT as the first item
in the initalization thread.
2. Move the eth_system_device_init into INIT_PREV_EXPORT item.

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;

fix memory leak in dfs_elm.c and umount fatfs when mount fatfs fails (this bug leads to mkfs failure in linux)

elm fatfs support mkfs with no need to  run dfs_mount elm first; and can mount/umount/mkfs without reset any more