LU-6047 mdt: remove Size on MDS support

LU-6047 mdt: remove Size on MDS support

Remove size on MDS support from lustre/mdt/. In struct mdt_object
change the struct mutex mot_ioepoch_mutex member to spinlock_t
mot_write_lock and rename mot_writecount to mot_write_count.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I271117618f7b88a22ddbcca4db5a4723ab48e3ea
Reviewed-on: http://review.whamcloud.com/13442
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>