btrfs: migrate to use per-fs workspace manager

There are several interfaces involved for each algorithm:

- alloc workspace
  All algorithms allocate a workspace without the need for workspace
  manager.
  So no change needs to be done.

- get workspace
  This involves checking the workspace manager to find a free one, and
  if not, allocate a new one.

  For none and lzo, they share the same generic btrfs_get_workspace()
  helper, only needs to update that function to use the per-fs manager.

  For zlib it uses a wrapper around btrfs_get_workspace(), so no special
  work needed.

  For zstd, update zstd_find_workspace() and zstd_get_workspace() to
  utilize the per-fs manager.

- put workspace
  For none/zlib/lzo they share the same btrfs_put_workspace(), update
  that function to use the per-fs manager.

  For zstd, it's zstd_put_workspace(), the same update.

- zstd specific timer
  This is the timer to reclaim workspace, change it to grab the per-fs
  workspace manager instead.

Now all workspace are managed by the per-fs manager.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>