LU-1346 libcfs: replace cfs_ memory wrappers

Replace memory relevant wrappers with kernel API.

Affected primitives:
CFS_PAGE_SIZE, CFS_PAGE_SHIFT, cfs_num_physpages,
cfs_copy_from_user, cfs_copy_to_user, cfs_page_address,
cfs_kmap/cfs_kunmap, cfs_get_page, cfs_page_count,
cfs_page_index, cfs_page_pin, cfs_page_unpin,
cfs_memory_pressure_get/set/clr, CFS_NUM_CACHEPAGES,
CFS_ALLOC_XXX flags, cfs_alloc/free, cfs_alloc/free_large,
cfs_alloc/free_page, CFS_DECL_MMSPACE, CFS_MMSPACE_OPEN,
CFS_MMSPACE_CLOSE, CFS_SLAB_XXX flags, cfs_shrinker_t,
cfs_set/remove_shrinker, CFS_DEFAULT_SEEKS, cfs_mem_cache_t,
cfs_mem_cache_alloc/free/create/destroy, cfs_mem_is_in_cache

manual changes:
1. cfs_alloc_flags_to_gfp() is removed
2. remove kmalloc/kfree etc. from linux-mem.c and linux-mem.h
3. remove page_address/kmap/kunmap etc. from linux-mem.h
4. remove page_cache_get/page_cache_release from echo_internal.h. They
are defined already in user-mem.h
5. change kmem_cache_create/destroy prototype to kernel's and modify
all callers to match them
6. define _SPL_KMEM_H and related macros to avoid using spl's
sys/kmem.h that redefines slab allocator
7. change kmem_virt to is_vmalloc_addr as provided by kernel, so that
we don't use any spl's sys/kmem.h functions
8. clean up include files a little bit in osd-zfs
9. various coding style cleanup

NUMA allocators(cfs_cpt_xxx) are not changed in this patch.
gnilnd is not converted, as requested by James Simmons.

Signed-off-by: Liu Xuezhao <xuezhao.liu@emc.com>
Signed-off-by: Peng Tao <tao.peng@emc.com>
Change-Id: Iadfbb0d5a0e31c78dd6c811e5ffdb468fa7e6f44
Reviewed-on: http://review.whamcloud.com/2831
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>