examples/vhost_crypto: support build with pkg-config
examples/vhost_crypto: support build with pkg-config

The vhost_crypto example app did not check for a libdpdk pkg-config file
and attempt to build using that. Add support for that method of compile to
align the app with the other examples.

Signed-off-by: Bruce Richardson <66b9e8e8fbd5e9f41f91b0af050876182ce9d0e4@intel.com>
Acked-by: Luca Boccassi <020748dc039465edc3ee6f30c530b21164cdce27@debian.org>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk