mem: support page locking on FreeBSD

mem: support page locking on FreeBSD

The function rte_mem_lock_page() was added for Linux only.
The file eal_common_memory.c is a better place to make it
available in FreeBSD also.

The issue is seen when trying to compile bnxt on FreeBSD:
	bnxt_hwrm.c: undefined reference to `rte_mem_lock_page'

Fixes: 3097de6e6bfb ("mem: get physical address of any pointer")

Reported-by: Fangfang Wei <fangfangx.wei@intel.com>
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>