* Simplify EINTR/ECANCEL error handling
1. Add semaphore uninterruptible wait function
2 .Replace semaphore wait loop with a single uninterruptible wait
3. Replace all sem_xxx to nxsem_xxx
* Unify the void cast usage
1. Remove void cast for function because many place ignore the returned value witout cast
2. Replace void cast for variable with UNUSED macro
fs/mount: Implements procfs /proc/fs/blocks and /proc/fs/usage files, replacing the NSH df command.
fs/mount: Implements procfs /proc/fs/mount file, replacing the NSH mount command when there are not arguments.
fs/: Move prototype of foreach_mountpoint out of include/nuttx/fs/fs.h to fs/mount/mount.h. Add framework for the mount procfs (initial commit is just a close of the net/route table procfs.
