dpdkbuild: always compile librte_kvargs

We need it to compile our internal rte_vhost, and
starting with DPDK 18.08 it's an EAL dependency.

Even though CONFIG_RTE_LIBRTE_KVARGS got commented out in
common_base, it's still hardcoded to =y in common_spdk
and that's why our autotest works.

Trying to build a DPDK target that doesn't use common_spdk
fails terribly right now, because other PMDs and libraries
that are built by default (defined in common_base) actually
depend on kvargs.

Change-Id: I171e768a75c6a460fc090ae3c9c65807eaec5945
Signed-off-by: Dariusz Stojaczyk <dariuszx.stojaczyk@intel.com>
Reviewed-on: https://review.gerrithub.io/422237


Chandler-Test-Pool: SPDK Automated Test System <sys_sgsw@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>