graphics/povray38: Remove NATIVE option and do some cleanups
- Drop NATIVE option, utilize CPUTYPE instead which is supported using the framework via /etc/make.conf
- Don't override optimization set by framework
- Utilize framework helpers more and do some slight rearrangement for better readability and consistency with Porters Handbook
PR: 273098
Reviewed by: Philipp Ost <bsd@philippost.de> (maintainer)
Sponsored by: Blinkinblox