nilfs2: persistent object allocator

This adds common functions to allocate or deallocate entries with bitmaps
on a meta data file.  This feature is used by the DAT and ifile.

Signed-off-by: Koji Sato <[email protected]>
Signed-off-by: Ryusuke Konishi <[email protected]>
Signed-off-by: Yoshiji Amagai <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: konis