vppinfra: Provide FreeBSD implementation of clib_mem functions

vppinfra: Provide FreeBSD implementation of clib_mem functions

Working from the implementation in linux/mem.c add FreeBSD specific
functionality. This duplicates parts of the Linux implementation and a
depuplication job could be run in the future.

Stub out some parts of the API for now, they are either use unavailable
features on FreeBSD or require further implementation than this initial
implementation.

Type: improvement
Change-Id: I1e443e32304d19776a9a4d5e34adfa16ec919427
Signed-off-by: Tom Jones <thj@freebsd.org>