psoc5lp: fix erase check, add free_driver_priv

psoc5lp: fix erase check, add free_driver_priv

psoc5lp_erase_check() was not properly adapted to the new
armv7m_blank_check_memory() in the hot fix 53376dbbede4f0bf42e724ff
This change fixes handling of num_sectors in dependecy of ecc_enabled.
Also add comments how ecc_enabled influences num_sectors.

Add pointer to default_flash_free_driver_priv() to all psoc5lp flash
drivers to keep valgrind happy.

Change-Id: Ie1806538becd364fe0efb7a414f0fe6a84b2055b
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/4569
Tested-by: jenkins