UBI: Fastmap: Add new module parameter fm_debug

If fm_debug is set fastmap debugging is enabled by default.
This is useful if one wants to debug fastmap on an UBI device
with serves the rootfs.
The the UBI attach mechanism runs long before debugfs can be mounted
and chk_fastmap set.

Signed-off-by: Richard Weinberger <richard@nod.at>
Git-commit: 479c2c0cac0c1d23655df15cf039b4f8e3623d23
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Nikhilesh Reddy <reddyn@codeaurora.org>