boards: nrf9161dk_nrf9161_ns: Add TF-M support to nrf9161 DK

Add TF-M support for nrf9161 DK and enable it by default for the
non-secure board variant.
Disable UART1 since TF-M use this for output and it is configured
as a secure peripheral.
Enabling this will trigger a BusFault in TF-M.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>