tests: aes: convert to ztest

- replaced test points with ztest APIs wherever possible
- replaced CONFIG_MAIN_STACK_SIZE with CONFIG_ZTEST_STACKSIZE
  in the config file
- split the main file into two files:
    - main.c has ztest entry and runs separate functions for ztest
    - aes.c has the original routines

JIRA: ZEP-2449

Signed-off-by: Niranjhana N <niranjhana.n@intel.com>