configs/imx8mn_bsh_smm_s2_defconfig: new defconfig

configs/imx8mn_bsh_smm_s2_defconfig: new defconfig

BSH SMM S2 (SystemMaster S2) Board is an add-on board which provide
input and output interfaces to a dedicated carrier board. It is designed
mainly to provide graphical/video and connectivity interfaces to the
appliance.

Board support package includes the following components:
- mainline Linux kernel 6.1.6
- mainline U-Boot 2022-07
- default packages from buildroot

https://www.apertis.org/reference_hardware/imx8mn_bsh_smm_s2pro_setup/
The smm s2 board is basically the same as the pro except it boots from
NAND instead of eMMC.

Co-authored-by: Michael Trimarchi <[email protected]>
Signed-off-by: Michael Trimarchi <[email protected]>
Signed-off-by: Dario Binacchi <[email protected]>
Reviewed-by: Giulio Benetti <[email protected]>
Signed-off-by: Thomas Petazzoni <[email protected]>