mtdparts: show net size in mtdparts list

This patch adds an additional column to the output of list_partitions. The
additional column will contain the net size and a '(!)' beside it if the net
size is not equal to the partition size.

Signed-off-by: Ben Gardiner <bengardiner@nanometrics.ca>
CC: Wolfgang Denk <wd@denx.de>
CC: Scott Wood <scottwood@freescale.com>