UBI: Fastmap fixes - round one

[Richard Weinberger]

This is the first set of fastmap fixes for v3.18.
I have more in my local queue but these depend on non-trivial
fastmap changes I made. As soon they have been fully tested I'll
submitt them too.

Thanks,
//richard

[PATCH 1/4] UBI: Ensure that all fastmap work is done upon WL
[PATCH 2/4] UBI: Fastmap: Calc fastmap size correctly
[PATCH 3/4] UBI: Fastmap: Care about the protection queue
[PATCH 4/4] UBI: Fastmap: Ensure that only one fastmap work is