LU-9679 libcfs: Add CFS_ALLOC_PTR_ARRAY and free

LU-9679 libcfs: Add CFS_ALLOC_PTR_ARRAY and free

Following the pattern of CFS_ALLOC_PTR() and the kernel
pattern of kmalloc_array(), add
  CFS_ALLOC_PTR_ARRAY()
and
  CFS_FREE_PTR_ARRAY()

which allocate and free arrays given a pointer to
the array, and a number of elements

This makes code easier to read and could be a step
toward using the kernel's hardened alloc_array interfaces,
which insure the multiplication doesn't overflow.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I54c919bd9ce22fbc72715c3da16f8c29e7135ccc
Reviewed-on: https://review.whamcloud.com/36975
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>