Kinetis: kinetis_ftfx_command() based on target instead of flash bank

Kinetis: kinetis_ftfx_command() based on target instead of flash bank

kinetis_ftfx_command() did not use other struct flash_bank* members
than base->target. Switching first parameter to struct target*
enables use of kinetis_ftfx_command() without unnecessary bank
getting and probing.

Removed kinetis_securing_test: kind of dead code, same function
as command flash erase_address pad 0x400 0x10

Removed "NAND" word from help as flash is obviously NOR

Change-Id: I3f5fc295ef2bf42f3e913549949f2a36377f6367
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/2988
Tested-by: jenkins