From Rohit Seth.

We're currently disabling read() and write() against hugetlbfs files via the
address_space ops.  But that's a bit awkward, and results in reads and writes
instantiating useless, non-uptodate 4k pagecache against the inodes.

The patch removes the read, write and sendfile file_operations entries.  So
the caller will get their -EINVAL without us ever having to go to the
pagecache layer.