dpdk: use vpp physmem allocator for dpdk buffers

dpdk: use vpp physmem allocator for dpdk buffers

This allows us to have single contignuous allocation for DPDK buffers
with single mmap FD, so buffer memory can be easily shared with diffrent
process.

As a consequence dpdk socket-mem is no longer in charge for allocating
buffer memory, but still we need some space allocated for dpdk
structures so default socket-mem is reduced form 256 to 64 MB.

For a default of 16K buffers per numa node, physmem allocation is now
40MB, so basically this change reduces footprint from 256MB per socket
to 48 (64 + 40).

Change-Id: Ic8cfe83930a18411545b37a12b14aac89affd04f
Signed-off-by: Damjan Marion <damarion@cisco.com>
Signed-off-by: Sergio Gonzalez Monroy <sergio.gonzalez.monroy@intel.com>
Signed-off-by: Damjan Marion <damarion@cisco.com>