xfs: separate out initial attr_set states

We current use XFS_DAS_UNINIT for several steps in the attr_set
state machine. We use it for setting shortform xattrs, converting
from shortform to leaf, leaf add, leaf-to-node and leaf add. All of
these things are essentially known before we start the state machine
iterating, so we really should separate them out:

XFS_DAS_SF_ADD:
	- tries to do a shortform add
	- on success -> done
	- on ENOSPC converts to leaf, -> XFS_DAS_LEAF_ADD
	- on error, dies.

XFS_DAS_LEAF_ADD:
	- tries to do leaf add
	- on success:
		- inline attr -> done
		- remote xattr || REPLACE -> XFS_DAS_FOUND_LBLK
	- on ENOSPC converts to node, -> XFS_DAS_NODE_ADD
	- on error, dies

XFS_DAS_NODE_ADD:
	- tries to do node add
	- on success:
		- inline attr -> done
		- remote xattr || REPLACE -> XFS_DAS_FOUND_NBLK
	- on error, dies

This makes it easier to understand how the state machine starts
up and sets us up on the path to further state machine
simplifications.

This also converts the DAS state tracepoints to use strings rather
than numbers, as converting between enums and numbers requires
manual counting rather than just reading the name.

This also introduces a XFS_DAS_DONE state so that we can trace
successful operation completions easily.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Allison <Henderson&lt;allison.henderson@oracle.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Dave Chinner <david@fromorbit.com>