Add an opt-in STM32N6_DEBUG setting to reopen the debug access port and
secure/non-secure debug at the current BSEC protection level. Enable the
BSEC clock and configure access before clock and memory initialization so
a debugger can attach to a flash-booted development image.
Assisted-by: Codex:GPT-6
Signed-off-by: raiden00pl <raiden00@railab.me>