UBI: Move fastmap specific functions out of wl.c

Fastmap is tightly connected to the WL sub-system, many fastmap-specific
functionslive in wl.c.
To get rid of most #ifdefs in wl.c move this functions into a new file
and include it into wl.c

Signed-off-by: Richard Weinberger <richard@nod.at>

diff --cc drivers/mtd/ubi/fastmap-wl.c
Simple merge

diff --cc drivers/mtd/ubi/wl.c
Simple merge

diff --cc drivers/mtd/ubi/wl.h
Simple merge