Make userspace tools number of fast commits blocks aware

Make userspace tools number of fast commits blocks aware

This patch makes number of fast commit blocks configurable. Also, the
number of fast commit blocks can now be seen in dumpe2fs output.

$ ./misc/mke2fs -O fast_commit -t ext4 image
mke2fs 1.46-WIP (20-Mar-2020)
Discarding device blocks: done
Creating filesystem with 5120 1k blocks and 1280 inodes
Allocating group tables: done
Writing inode tables: done
Creating journal (1040 blocks): done
Writing superblocks and filesystem accounting information: done

$ ./misc/dumpe2fs image
dumpe2fs 1.46-WIP (20-Mar-2020)
...
Journal features:         (none)
Total journal size:       1040k
Total journal blocks:     1040
Max transaction length:   1024
Fast commit length:       16
Journal sequence:         0x00000001
Journal start:            0

$ ./misc/mke2fs -O fast_commit -t ext4 image -J fast_commit_size=256,size=1
mke2fs 1.46-WIP (20-Mar-2020)
Creating filesystem with 5120 1k blocks and 1280 inodes
Allocating group tables: done
Writing inode tables: done
Creating journal (1280 blocks): done
Writing superblocks and filesystem accounting information: done

$ ./misc/dumpe2fs image
dumpe2fs 1.46-WIP (20-Mar-2020)
...
Journal features:         (none)
Total journal size:       1280k
Total journal blocks:     1280
Max transaction length:   1024
Fast commit length:       256
Journal sequence:         0x00000001
Journal start:            0

This patch also adds information about fast commit feature in mke2fs
and tune2fs man pages.

Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>