devel/libnvme: Fix port

• Use DISTVERSION (and consistent)
• Fix COMMENT
• Define LICENSE_FILE
• Remove CXXFLAGS, project uses C
• Simplify MAJORVER definition
• Adjust pkg-descr
• Rearrange Makefile so it follows Porters Handbook more closely

Poudriere testport OK 14.2-RELEASE and 13.4-RELEASE

PR: 284970
Reviewed by: imp