petitboot: Explicitly enable Busybox support

Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
diff --git a/openpower/package/petitboot/petitboot.mk b/openpower/package/petitboot/petitboot.mk
index 2f13eb5..a4c8aa7 100644
--- a/openpower/package/petitboot/petitboot.mk
+++ b/openpower/package/petitboot/petitboot.mk
@@ -17,7 +17,7 @@
 	      --localstatedir=/var \
 	      HOST_PROG_KEXEC=/usr/sbin/kexec \
 	      HOST_PROG_SHUTDOWN=/usr/libexec/petitboot/bb-kexec-reboot \
-	      $(if $(BR2_PACKAGE_BUSYBOX),--with-tftp=busybox)
+	      $(if $(BR2_PACKAGE_BUSYBOX),--with-tftp=busybox --enable-busybox)
 
 PETITBOOT_AUTORECONF_ENV += PETITBOOT_VERSION=`cat $(PETITBOOT_VERSION_FILE) | cut -d '-' -f 2-`