Mass erase operation might be impacted by different factors,
apparently the most reliable way is to do it while asserting the chip
reset line.
Change-Id: Id6ab57eaec86e402ffdf4f5c8843e7735640f03e
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2424
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>