UBI: power cut emulation for testing

Emulate random power cuts by switching device to ro after a number of
writes to allow simple power cut testing with nand-sim.

Maximum and minimum number of successful writes before power cut and
what kind of writes (EC header, VID header or none) to interrupt
configurable via debugfs.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>
Signed-off-by: Richard Weinberger <richard@nod.at>

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

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

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

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