eal/freebsd: fix IOVA mode selection

eal/freebsd: fix IOVA mode selection

FreeBSD EAL selected IOVA mode PA even in --no-huge mode
where PA are not available. Memory zones were created with IOVA
equal to RTE_BAD_IOVA with no indication this field is not usable.

Change IOVA mode detection:
1. Always allow to force --iova-mode=va.
2. In --no-huge mode, disallow forcing --iova-mode=pa, and select VA.
3. Otherwise select IOVA mode according to bus requests, default to PA.
In case contigmem is inaccessible, memory initialization will fail
with a message indicating the cause.

Fixes: c2361bab70c5 ("eal: compute IOVA mode based on PA availability")
Cc: stable@dpdk.org
Signed-off-by: Dmitry Kozlyuk <dkozlyuk@nvidia.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>