Fastmap update v2 (pile 4)

[Richard Weinberger]

Artem,

this is pile 4 of 7.

[PATCH 1/6] UBI: Fastmap: Fix leb_count unbalance
[PATCH 2/6] UBI: Fastmap: Fix race after ubi_wl_get_peb()
[PATCH 3/6] UBI: Fastmap: Set used_ebs only for static volumes
[PATCH 4/6] UBI: Fastmap: Locking updates
[PATCH 5/6] UBI: Fastmap: Prepare for variable sized fastmaps
[PATCH 6/6] UBI: Fastmap: Rework fastmap error paths

Thanks,
//richard