LU-506 kernel: remove BKL

LU-506 kernel: remove BKL

Late kernel removes BKL completely; do so for lustre:
* replace BKL with inode->i_lock in ldiskfs.
* HAVE_UNLOCKED_IOCTL is defined after 2.6.12, so this check can be
  removed from lustre code now.
* remove all lock/unlock_kernel definition/usage from lustre code.
* check kernel_locked() in configure, which is removed in 2.6.37.

Signed-off-by: Lai Siyao <laisiyao@whamcloud.com>
Change-Id: I8a3432ad56b7a1fcdbf74be4b7819edb31bf6272
Reviewed-on: http://review.whamcloud.com/2169
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>