tests: arm_irq_vector_table: convert to ztest

- file already had ztest functions
- separated the main file into two:
    - main.c, which has the ztest entry
    - arm_irq_vector_table.c, which has the original routines

JIRA: ZEP-2382

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