devel/p4 devel/p4api: build from source

Build devel/p4 and devel/p4api from source rather than use the prebuilt
binary downloads. This fixes p4api on FreeBSD 12. The ports originally used
the binaries because source wasn't available until a few years ago. By
happy accident, building from source also makes the ports available on
non-Intel architectures.

PR: 225613
Reviewed by: brd
Approved by: brd (ports)
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D14162