fs: break out inode operations from inode_lock V3

[Dave Chinner <david@fromorbit.com>]

Hi Al,

This series is a merge of the two previous sets of patches that
broke the inode LRU operations and the first half of iput_final()
out from under the inode_lock and then split the lists under
separate locks.  The patches should apply to your current merge-stem
tree. I can rebase it on a different tree if you want.

Version 3:
- remove up wake_up_inode() inode_lock avoidance optimisation as the
  inode_lock is no longer protecting i_state.
- Added a BUG_ON() check to evict() to ensure that inodes are removed
  from the LRU before being evicted.
- removed inode_lock from igrab() when removing inode_lock from the
  first half of iput_final()
- added 3 patches to convert the per-sb inode list, the writeback lists and the
  inode hashes under their own locks. The changes from the first version of
  these patches (posted separately) are:
	- cleaned up comment for writeback_single_inode()
	- dropped __mark_inode_dirty() cleanup and just moved the minimum
	  amount of code around to handle the locking changes cleanly.
	- moved adding inodes to sb list under the hash lock as well so we
	  don't have inodes that are not on the per-sb lists on the hash.
- added a patch to clean up inode_lock references in documentation and
  comments.

Version 2:
- make i_state checks/__iget() atomic under inode->i_lock
- merge dispose_one_inode() into evict()
- move inode hash removal after ->evict_inode call.
- always take the inode_lru_lock() when checking whether the inode
  is on the lru or not.