build: replace phony target with .ok file

build: replace phony target with .ok file

When VPP builds its external packages from source, it will download the
package, patch it, configure it, build and install it. For DPDK, it will
depend on rdma-core if mlx4/mlx5 PMD is enabled. So phony target
dpdk-config needs to have the prerequisites of rdma-core-install and
ipsec-mb-install(x86 only), which are both phony targets. This leads to
redundant behavior of recipes executing twice in dpdk-config.
Replace the phony target with hidden file *.install.ok to avoid that.

Type: improvement
Signed-off-by: Lijian Zhang <lijian.zhang@arm.com>
Signed-off-by: Jieqiang Wang <jieqiang.wang@arm.com>
Change-Id: Ibf3b766ab7a4ccfcbffe08f6cdb90da72ca1ce29