vhost: remove async DMA map status

vhost: remove async DMA map status

Async DMA map status flag was added to prevent the unnecessary unmap
when DMA devices bound to kernel driver. This brings maintenance cost
for a lot of code. This patch removes the DMA map status by using
rte_errno instead.

This patch relies on the following patch to fix a partial
unmap check in vfio unmapping API.
[1] https://www.mail-archive.com/dev@dpdk.org/msg226464.html

Signed-off-by: Xuan Ding <xuan.ding@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>