Add btrfs file item tracepoints

Add btrfs file item tracepoints

See upstream commit:

  commit 09ed2f165cb3449237dec842b3564044e12d22cb
  Author: Liu Bo <bo.li.liu@oracle.com>
  Date:   Fri Mar 10 11:09:48 2017 -0800

    Btrfs: add file item tracepoints

    While debugging truncate problems, I found that these tracepoints could
    help us quickly know what went wrong.

    Two sets of tracepoints are created to track regular/prealloc file item
    and inline file item respectively, I put inline as a separate one since
    what inline file items cares about are way less than the regular one.

    This adds four tracepoints:
    - btrfs_get_extent_show_fi_regular
    - btrfs_get_extent_show_fi_inline
    - btrfs_truncate_show_fi_regular
    - btrfs_truncate_show_fi_inline

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>