nilfs2: use common file attribute macros

Replaces uses of own inode flags (i.e. NILFS_SECRM_FL, NILFS_UNRM_FL,
NILFS_COMPR_FL, and so forth) with common inode flags, and removes the
own flag declarations.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>