M2351: Re-build default secure program to favor Pelion application

In this new memory partition, secure program is most simplified and non-secure program can make most use of memory for its large application like Pelion:

-   Flash (512KiB in total): 64KiB for secure and 448KiB for nonsecure.
-   SRAM (96KiB in total): 8KiB for secure and 88KiB for nonsecure.

Author: ccli8