pnfsblock: add blocklayout Kconfig option, Makefile, and stubs

Define a configuration variable to enable/disable compilation of the
block driver code.

Add the minimal structure for a pnfs block layout driver, and empty
list-heads that will hold the extent data

[pnfsblock: make NFS_V4_1 select PNFS_BLOCK]
Signed-off-by: Peng Tao <peng_tao@emc.com>
Signed-off-by: Fred Isaman <iisaman@citi.umich.edu>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
[pnfs-block: fix CONFIG_PNFS_BLOCK dependencies]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Benny Halevy <bhalevy@tonian.com>
[pnfsblock: SQUASHME: adjust to API change]
Signed-off-by: Fred Isaman <iisaman@citi.umich.edu>
[pnfs: move pnfs_layout_type inline in nfs_inode]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
[blocklayout: encode_layoutcommit implementation]
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Benny Halevy <bhalevy@tonian.com>
[pnfsblock: layout alloc and free]
Signed-off-by: Fred Isaman <iisaman@citi.umich.edu>
[pnfs: move pnfs_layout_type inline in nfs_inode]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Benny Halevy <bhalevy@tonian.com>
[pnfsblock: define module alias]
Signed-off-by: Peng Tao <peng_tao@emc.com>
[rm inode and pnfs_layout_hdr args from cleanup_layoutcommit()]
Signed-off-by: Jim Rees <rees@umich.edu>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>