flash/nor: improved API of flash_driver.info & fixed buffer overruns

flash/nor: improved API of flash_driver.info & fixed buffer overruns

1) The API of "info" callback in "struct flash_driver" has been
improved. Fixed buffers for strings

2) Removed the calls to snprintf() from the flash_driver.info
implementations. Many of them were used in an unsafe manner
(buffer overruns were possible).

Change-Id: I42ab8a8018d01f9af43c5ba49f650c3cb5d31dcb
Signed-off-by: Jan Matyas <matyas@codasip.com>
Reviewed-on: http://openocd.zylin.com/6182
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>