[PATCH RFC v2] ubi-utils: Introduce a utility ubidump

[hujianyang]

Hi all,

After discussing with Artem, I've applied some of his ideas and
rewrite this utility.

Bill also gives me help. I reference his code about getting data
from MTD device.

Thank you all~!

v1:
http://lists.infradead.org/pipermail/linux-mtd/2014-July/054541.html

Changes in v2:
 - modified ioctl() in ubi_vol which just return pnum now.
 - change libubifs.c/libubifs.h into libdump.c/libdump.h and
   remove ubi-level header dump function into libdump.c.
 - read data in eraseblock from MTD functionality.
 - add a new function "ubidump" to handle peb dumping.
 - modified options -H/-N into --ubi/--ubifs.

I found this utility can't dump lpt area correctly because we use
different structure to format this area. I will enable it soon. I
think we should confirm the mechanism of this utility first.