boards: b_u585i_iot02a: Add a non-secure target Provide a _ns target for b_u585i_iot02a board. Flash partition is given as default for most applications, with the following sizes: MCUBoot: 208K Secure: 256K Non secure: 512K Tested using tfm_ipc sample. Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>