fix(setup_board): Depend on --usepkg and --getbinpkg as a pair.

Instead of gating only on --usepkg depend on both flags as a pair. This
keeps setup_board's behavior a little closer to build_packages. The
buildbot is using --nogetbinpkg to avoid pulling in existing packages
built by the SDK but setup_board is causing some to be pulled in anyway.
fix(toolchain_util.sh): Never force binary packages with crossdev.

When calling update_chroot with --usepkg --nogetbinpkg the default
emerge command line will force binary packages for the toolchain but if
the packages are not available locally building via crossdev is
required. Since the crossdev bootstrap process rebuilds the toolchain a
couple times with different use flags if binary packages are forced the
second stages gets skipped resulting in a broken gcc and glibc install.
Merge pull request #140 from marineam/fixpkgmixups

Fix building w/ --nogetbinpkg