flash/nor: implement flash bank deallocation in drivers with simple alloc

flash/nor: implement flash bank deallocation in drivers with simple alloc

All drivers which simply allocate one driver_priv memory block
per each bank now use default_flash_free_driver_priv()

Change-Id: I425bf4213c3632f02dbe11ab819c31eda9b2db62
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/4417
Tested-by: jenkins
Reviewed-by: Liviu Dudau <liviu@dudau.co.uk>
Reviewed-by: Matthias Welwarsky <matthias@welwarsky.de>