mtd: ofpart: support partitions of 4 GiB and larger

Previously, partitions were limited to less than 4 GiB in size because
the address and size were read as 32-bit values. Add support for 64-bit
values to support devices of 4 GiB and larger.

Signed-off-by: Joe Schaack <jschaack@xes-inc.com>
Signed-off-by: Nate Case <ncase@xes-inc.com>
Signed-off-by: Aaron Sierra <asierra@xes-inc.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>