bsd.progs.mk: Create directories first

Order installdirs before the $p.install targets; this is necessary
when a user of <bsd.progs.mk> also creates the directory into which
the binaries are installed.

In particular, without this patch running make installworld -jN can
break when installing tests since the /usr/tests/foo/bar directories
are created during installworld; this has been causing the stable/14
weekly snapshot builds to intermittently fail for months.

MFC after: 5 minutes
Sponsored by: Amazon
Differential Revision: https://reviews.freebsd.org/D45923