build-setup: use `setup` instead of direct source

There is a large case statement in this script to codify the
"supported" machines and the location of their layer directory.
Much of this information is already handled by the `setup` script
found in the root of the openbmc repository.  Rather than
duplicating this information here, use the setup script directly.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: If0b3a204dd895ba965055750f1381e50e8c461e4
diff --git a/build-setup.sh b/build-setup.sh
index dbee5c5..575b3a1 100755
--- a/build-setup.sh
+++ b/build-setup.sh
@@ -217,7 +217,7 @@
     ;;
 esac
 
-BITBAKE_CMD="TEMPLATECONF=${LAYER_DIR}/conf source oe-init-build-env"
+BITBAKE_CMD="source ./setup ${MACHINE} ${build_dir}"
 
 # Configure Docker build
 if [[ "${distro}" == fedora ]];then