boards: lpcxpress55s69: NS target with TFM support

Configures the Non-Secure target to work with TFM.
Memory (Flash and RAM) mapping according to TFM definitions.
How to build and flash the board.

Signed-off-by: Andrei Gansari <andrei.gansari@nxp.com>
Signed-off-by: Kevin Townsend <kevin@ktownsend.com>