Linux_5.0: replace do_gettimeofday with ktime_get_real_ts64

Linux_5.0: replace do_gettimeofday with ktime_get_real_ts64

In Kernel commit e4b92b108c6cd6b311e4b6e85d6a87a34599a6e3 the
do_gettimeofday function was removed.

According to the Linux Documentation/core-api/timekeeping.rst
ktime_get_real_ts64 is the direct replacement for do_gettimeofday

Updated the macro osi_GetTime to use ktime_get_real_ts64 if it is
available.

Change-Id: I7fcd49958de83a6a040e40bd310a228247c481b2
Reviewed-on: https://gerrit.openafs.org/13433
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>