LU-1389 lov: standardize lov_do_div64() usage

LU-1389 lov: standardize lov_do_div64() usage

Rename ll_do_div64() to lov_do_div64() and move it to a header
for use by LOV and LOD.  Lustre shouldn't use linux-specific
methods in the code, so this is a bit of portability fix as well.

Change-Id: Ia6f071914a982c7c7d5f2d11271f9587aea01ed6
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-on: http://review.whamcloud.com/1619
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>