Disabled nfp build in FreeBSD because it is not supported
Added changes to enable NFP build if it is Linux OS and
disable in FreeBSD.
Fixes: d9b9ca7e0595 ("net/nfp: add to meson build")
Cc: stable@dpdk.org
Signed-off-by: Agalya Babu RadhaKrishnan <agalyax.babu.radhakrishnan@intel.com>