tfm: Change TFM_BL2 config from a choice to a bool

The choice allowed for using TFM's own default. We now need full
knowledge over whether BL2 is enabled or not (e.g. to do signing),
so remove this option and simplify to a bool.

Signed-off-by: Øyvind Rønningstad <oyvind.ronningstad@nordicsemi.no>
6 files changed