eal: add single file segments option

eal: add single file segments option

Currently, DPDK stores all pages as separate files in hugetlbfs.
This option will allow storing all pages in one file (one file
per memseg list).

We do this by using fallocate() calls on FreeBSD, however this is
only supported on fairly recent (4.3+) kernels, so ftruncate()
fallback is provided to grow (but not shrink) hugepage files.
Naming scheme is deterministic, so both primary and secondary
processes will be able to easily map needed files and offsets.

For multi-file segments, we can close fd's right away. For
single-file segments, we can reuse the same fd and reduce the
amount of fd's needed to map/use hugepages. However, we need to
store the fd's somewhere, so we add a tailq.

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
Tested-by: Santosh Shukla <santosh.shukla@caviumnetworks.com>
Tested-by: Hemant Agrawal <hemant.agrawal@nxp.com>
Tested-by: Gowrishankar Muthukrishnan <gowrishankar.m@linux.vnet.ibm.com>