LU-12355 llite: totalram_pages changed to atomic_long_t

LU-12355 llite: totalram_pages changed to atomic_long_t

Kernel 5.0 changed totalram_pages to atomic_long_t
Provide an abstracted accessor now that totalram_pages
is now a function

Linux-commit: ca79b0c211af63fa3276f0e3fd7dd9ada2439839

Test-Parameters: trivial
Change-Id: I558e42074004e2ee5f79deea0d363e5bea332729
Signed-off-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-on: https://review.whamcloud.com/35025
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Petros Koutoupis <pkoutoupis@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>