zephyr: clean up Kconfig file
zephyr: clean up Kconfig file

The kconfig file is a bit disorderly. Clean it up. There are no
changes in this commit which affect the bootloader's behavior.

Signed-off-by: Marti Bolivar <fd5da480b758a78208111e6ae5c6806e1f887137@opensourcefoundries.com>

ATmobica/mcuboot,ATmobica/mcuboot,runtimeco/mcuboot,utzig/mcuboot,utzig/mcuboot,tamban01/mcuboot,tamban01/mcuboot,tamban01/mcuboot,utzig/mcuboot,ATmobica/mcuboot,tamban01/mcuboot,runtimeco/mcuboot,runtimeco/mcuboot,runtimeco/mcuboot,utzig/mcuboot,utzig/mcuboot,tamban01/mcuboot,runtimeco/mcuboot,ATmobica/mcuboot,ATmobica/mcuboot