mtd-utils: nandtest: handle large nand devices

mtd-utils: nandtest: handle large nand devices

Running nandtest on devices with sizes of 4Gb or more does not work, as
the size returned in mtd_info_user is reported as 0 for 4Gb devices for
example.

The patch uses sysfs to figure out the size of the nand device (as
recommended in a comment in include/mtd/mtd-abi.h) and changes sizes
and offsets to 64 bit values.

[From: Christian Wendt <cw@brainaid.de>]
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>