devel/p4 devel/p4api: use the source

Build devel/p4 and devel/p4api from source rather than use the prebuilt
binary downloads. This fixes p4api on FreeBSD 12. By happy accident, it
also makes the ports available on non-Intel architectures.

PR: 225613

Used the new p4api to build rubygem-p4ruby and ran a simple program with it.