[PATCH 1/7] UBI: Add a new ioctl to support ubidump

[hujianyang]

Hi Artem,

Thank you for reviewing these patches.

> 
> Do you really need to dump UBI headers?
>

Yes, because I think ec_counter in ec_hdr and copy_flag, sqnum
in vid_hdr are useful.

Current ->read() can just read data from data_offset where the
leb located. And reading UBI headers by mtd functionality are
very complicated, we don't know pnum either.

Maybe we can try other way instead of this ioctl, by adding an
new function which can read the hole peb specified by lnum to
user space.