MFH: r392478

Update to devel/p4 2015.1/1126382 to fix broken port.
Migrate common variable for the devel/p4* ports into the Makefile.inc.

PR: 201216
Differential Revision: https://reviews.freebsd.org/D3088
Approved by: mat (mentor)
Approved by: ports-secteam (feld)