vfio: add stdbool include

vfio: add stdbool include

This became visible by backporting the following for the 19.11 stable tree:
 c13ca4e8 "vfio: fix DMA mapping granularity for IOVA as VA"

The usage of type bool in the vfio code would require "#include
<stdbool.h>", but rte_vfio.h has no direct paths to stdbool.h.
It happens that in eal_vfio_mp_sync.c it comes after "#include
<rte_log.h>".

And rte_log.h since 20.05 includes stdbool since this change:
 241e67bfe "log: add API to check if a logtype can log in a given level"
and thereby mitigates the issue.

It should be safe to include stdbool.h from rte_vfio.h itself
to be present exactly when needed for the struct it defines using that
type.

Fixes: c13ca4e81cac ("vfio: fix DMA mapping granularity for IOVA as VA")
Cc: stable@dpdk.org
Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>