setup_board: add more vars

BUG=b:20895978
diff --git a/setup_board b/setup_board
index 2d93c2e..099b926 100755
--- a/setup_board
+++ b/setup_board
@@ -91,6 +91,7 @@
 CHOST="x86_64-cros-linux-gnu"
 MAKEOPTS="-j%(ncpus)i"
 PKG_CONFIG="${SYSROOT}/build/bin/pkg-config"
+PKGDIR="${SYSROOT}/packages"
 PORTDIR_OVERLAY="${SOURCE_ROOT}/src/third_party/eclass-overlay
 ${SOURCE_ROOT}/src/third_party/portage-stable
 ${SOURCE_ROOT}/src/third_party/chromiumos-overlay