vfio: disable in FreeBSD build with meson

vfio: disable in FreeBSD build with meson

FreeBSD compilation was failing through meson build.
RTE_EAL_VFIO is not supported in FreeBSD.
But RTE_EAL_VFIO was enabled for both linux and freebsd.
So RTE_EAL_VFIO is removed from config/rte_config.h and
based on the platform RTE_EAL_VFIO flag is enabled/disabled appropriately.

Fixes: 844514c735 ("eal: build with meson")
Cc: stable@dpdk.org
Signed-off-by: Agalya Babu RadhaKrishnan <agalyax.babu.radhakrishnan@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>