Add springbok vector unit test for vmerge

Added a simple vector unit test for vmerge operations to verify if vmerge.vim and vmerge.vvm work properly.

Test results:
- vmerge.vim and vmerge.vvm tests passed for Qemu and Renode.

Change-Id: Id6108ed7577cdc159de2b602ec2b806a39f7e7f5