Patch from Badari Pulavarty <pbadari@us.ibm.com> and myself

This patch adds the infrastructure for performing asynchronous (AIO) blockdev
direct-IO.

- Adds generic_file_aio_write_nolock() and make other
  generic_file_*_write() to use it.

- Modify generic_file_direct_IO() and ->direct_IO() functions to take
  "kiocb *" instead of "file *".

- Renames generic_direct_IO() to blockdev_direct_IO().

- Move generic_file_direct_IO() to mm/filemap.c (it is not
  blockdev-specific, whereas the rest of fs/direct-io.c is).

- Add AIO read/write support to the raw driver.