mtd: part: Add sysfs variable for offset of partition

This patch makes a sysfs variable called 'offset' on each partition
which contains the offset in bytes from the beginning of the master
device that the partition starts.

Signed-off-by: Dan Ehrenberg <dehrenberg@chromium.org>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

diff --cc Documentation/ABI/testing/sysfs-class-mtd
Simple merge

diff --cc drivers/mtd/mtdpart.c
Simple merge