CVL Changes #1: Initial CVL code reorganization and common infra changes

[dutta-partha]

- Why I did it

As part of CVL code update and new features addition, the existing CVL code has to be reorganized and common infra needs to be changed.

- How I did it

N/A.
Please refer to change log for more details.

- How to verify it

No specific test cases to be executed. Run cvl go test cases using - 'make cvl-test'.

- Description for the changelog

1. Modify Makefiles
   • Modify CVL Makefile for cleanall rule
   • Modify Makefile for CVL YIN schema generation
   • Modify Makefile for CVL test YIN schema generation
2. Moved cache, syntax and semantic related code from cvl.go to cvl_cache.go, cvl_syntax.go and cvl_semantics.go respectively .
3. Added new API signatures for integration. Implementation will be added in subsequent PRs.
4. Copied sonic-port.yang and sonic-acl.yang to CVL own's test folder.