pnfs/flexfiles: Add the FlexFile Layout Driver

The flexfile layout is a new layout that extends the
file layout. It is currently being drafted as a specification at
https://datatracker.ietf.org/doc/draft-ietf-nfsv4-layout-types/

Signed-off-by: Weston Andros Adamson <dros@primarydata.com>
Signed-off-by: Tom Haynes <loghyr@primarydata.com>
Signed-off-by: Tao Peng <bergwolf@primarydata.com>

diff --cc fs/nfs/Kconfig
Simple merge

diff --cc fs/nfs/Makefile
Simple merge

diff --cc fs/nfs/flexfilelayout/Makefile
Simple merge

diff --cc fs/nfs/flexfilelayout/flexfilelayout.c
Simple merge

diff --cc fs/nfs/flexfilelayout/flexfilelayout.h
Simple merge

diff --cc fs/nfs/flexfilelayout/flexfilelayoutdev.c
Simple merge

diff --cc fs/nfs/idmap.c
Simple merge

diff --cc fs/nfs/nfs4proc.c
Simple merge

diff --cc fs/nfs/pnfs.c
Simple merge

diff --cc fs/nfs/pnfs.h
Simple merge

diff --cc include/linux/nfs4.h
Simple merge

diff --cc include/linux/nfs_idmap.h
Simple merge

diff --cc include/linux/sunrpc/metrics.h
Simple merge