CMakeLists.txt: Updated the rule for shared memory alignment.

Due to the new changes for the subsys/app_memory we need to
have the script for smem run before any elf is created.
This is needed because the compiled code will have references to
certain linker variables that will be created by
gen_app_partitions.py.

Signed-off-by: Adithya Baglody <adithya.nagaraj.baglody@intel.com>