LU-6245 libcfs: add ktime_get_real_seconds support

LU-6245 libcfs: add ktime_get_real_seconds support

In newer kernels time support is moving to u64 to avoid
the 2038 limitation. The function get_seconds() which
only returns a 32 bit value is being replaced by a new
function ktime_get_real_seconds(). This patch adds a
wrapper for older platforms that lack this function.
Only the libcfs/LNet layer has been ported in this
patch since it is a huge change.

Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Change-Id: Ic16859f1b052bfb72299cc85fe50364a9e70d660
Reviewed-on: https://review.whamcloud.com/22866
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Frank Zago <fzago@cray.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>