fs: introduce f_op->mmap_capabilities for nommu mmap support

Since "BDI: Provide backing device capability information [try #3]" the
backing_dev_info structure also provides flags for the kind of mmap
operation available in a nommu environment, which is entirely unrelated
to it's original purpose.

Introduce a new nommu-only file operation to provide this information to
the nommu mmap code instead.  Splitting this from the backing_dev_info
structure allows to remove lots of backing_dev_info instance that aren't
otherwise needed, and entirely gets rid of the concept of providing a
backing_dev_info for a character device.  It also removes the need for
the mtd_inodefs filesystem.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Tejun Heo <tj@kernel.org>
Acked-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --cc Documentation/nommu-mmap.txt
Simple merge

diff --cc block/blk-core.c
Simple merge

diff --cc drivers/char/mem.c
Simple merge

diff --cc drivers/mtd/mtdchar.c
Simple merge

diff --cc drivers/mtd/mtdconcat.c
Simple merge

diff --cc drivers/mtd/mtdcore.c
Simple merge

diff --cc drivers/mtd/mtdpart.c
Simple merge

diff --cc drivers/staging/lustre/lustre/llite/llite_lib.c
Simple merge

diff --cc fs/9p/v9fs.c
Simple merge

diff --cc fs/afs/volume.c
Simple merge

diff --cc fs/aio.c
Simple merge

diff --cc fs/btrfs/disk-io.c
Simple merge

diff --cc fs/char_dev.c
Simple merge

diff --cc fs/cifs/connect.c
Simple merge

diff --cc fs/coda/inode.c
Simple merge

diff --cc fs/configfs/configfs_internal.h
Simple merge

diff --cc fs/configfs/inode.c
Simple merge

diff --cc fs/configfs/mount.c
Simple merge

diff --cc fs/ecryptfs/main.c
Simple merge

diff --cc fs/exofs/super.c
Simple merge

diff --cc fs/ncpfs/inode.c
Simple merge

diff --cc fs/ramfs/file-nommu.c
Simple merge

diff --cc fs/ramfs/inode.c
Simple merge

diff --cc fs/romfs/mmap-nommu.c
Simple merge

diff --cc fs/ubifs/super.c
Simple merge

diff --cc include/linux/backing-dev.h
Simple merge

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

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

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

diff --cc mm/backing-dev.c
Simple merge

diff --cc mm/nommu.c
Simple merge

diff --cc security/security.c
Simple merge