UBI: add UBI devices reference counting

This is one more step on the way to "removable" UBI devices. It
adds reference counting for UBI devices. Every time a volume on
this device is opened - the device's refcount is increased. It
is also increased if someone is reading any sysfs file of this
UBI device or of one of its volumes.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

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

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

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

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

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

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

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