ubifs-utils: Decouple mkfs.ubifs.h out of other modules

ubifs-utils: Decouple mkfs.ubifs.h out of other modules

Header file mkfs.ubifs.h is included in other modules(eg. compr.c, lpt.c,
fscrypt.h, sign.c), decouple it out of other modules.

There are two parts in mkfs.ubifs.h:
1. common functions, for example dbg_msg, err_msg and write_leb, move
   these functions into common/defs.h and common/ubifs.h.
2. devtable related definations, move them into a new header file
   common/devtable.h.

Splitting common functions from mkfs.ubifs.h is also a preparation for
importing libubifs(from linux kernel) to replace current UBIFS libs.

Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>