lang/php7*: disable DTRACE on powerpc64
php ports don't build on elfv2 with DTRACE.
PR: 242113, 242114, 242116
Approved by: tz (maintainer), tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D22577
Differential Revision: https://reviews.freebsd.org/D22578
Differential Revision: https://reviews.freebsd.org/D22579