A subset of the dpdk headers are arch-dependent, but have common names
and thus cause a clash in a multiarch installation.
For example, rte_config.h is different for each target.
Add a "include_subdir_arch" option to allow a user to specify a
subdirectory for arch independent headers to fix multiarch support.
Signed-off-by: Luca Boccassi <bluca@debian.org> Acked-by: Bruce Richardson <bruce.richardson@intel.com>