LU-709 build: cleanup LC_SEQ_LOCK/FILEMAP_FDATAWRITE_RANGE

LU-709 build: cleanup LC_SEQ_LOCK/FILEMAP_FDATAWRITE_RANGE

1. struct seq_file has lock instead of semaphore since v2.6.17
   and seq_file lock is not used in Lustre
2. filemap_fdatawrite_range is exported since v2.6.27
   andRHEL v2.6.18 back ported it. So all kernels Lustre
   supports now have it.

Signed-off-by: Peng Tao <peng_tao@emc.com>
Change-Id: I5730852789a5c19350eebb65fd61baf2a6512626
Reviewed-on: http://review.whamcloud.com/2321
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>