LU-1756 kernel: cleanup lustre_compat25.h

1. unused functions:
   ll_bdi_wb_cnt()
2. call bdi_init/bdi_destroy directly
3. call add_to_page_cache_lru directly
4. fix a typo of ll_pagevec_init
5. remove QUOTA_OK/NO_QUOTA. They are defined in libcfs

Signed-off-by: Peng Tao <tao.peng@emc.com>
Change-Id: I9953dabbc758e6fb7a3d0649bdc64ba1455efb99
Reviewed-on: http://review.whamcloud.com/3689
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>