vhost: fix linkage of driver with library

vhost: fix linkage of driver with library

Currently, vhost PMD doesn't have linkage for librte_vhost, even though
it depends on librte_vhost APIs. This causes a linkage error if below
conditions are fulfilled.

 - DPDK libraries are compiled as shared libraries.
 - DPDK application doesn't link librte_vhost.
 - Above application tries to link vhost PMD using '-d' DPDK option.

The patch adds linkage for librte_vhost to vhost PMD not to cause an
above error.

Fixes: ee584e9710b9 ("vhost: add driver on top of the library")

Signed-off-by: Tetsuya Mukawa <mukawa@igel.co.jp>
Acked-by: Panu Matilainen <pmatilai@redhat.com>
Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>