flash/nor: use command_print() in command "flash banks"

flash/nor: use command_print() in command "flash banks"

The command uses LOG_USER() instead of command_print().
Fix it.

This change was part of http://openocd.zylin.com/1815 from Paul
Fertser and has been extracted and rebased to simplify the review.

Change-Id: I92e5e5954a75b96093b3ed6af73a7536c063b639
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5083
Tested-by: jenkins