staging/lustre: Always try kmalloc first for OBD_ALLOC_LARGE

Create libcfs_kvzalloc and libcfs_kvzalloc_cpt that
are designed to replace OBD_ALLOC_LARGE and OBD_CPT_ALLOC_LARGE.

Not a drop-in replacement as they also take gfp flags armument
for more flexibility.

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>