LU-8560 libcfs: handle page_cache_*() removal in newer kernels

Since page cache handling never was handled differently than
normal pages the page_cache_*() macros have been removed
starting with linux kernel 4.6. Now put_page() and get_page()
need to be used instead.

Second change is that get_user_page dropped the first two
arguments in linux kernel version 4.6. We handle this change
as well in libcfs.

Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Change-Id: I84c347a55c45e0794b913134f1abdd45926c24e8
Reviewed-on: http://review.whamcloud.com/22385
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>