cmfs: copy & modify masklog code from ocfs2

This patch copies masklog.c and masklog.h from ocfs2 code.
Since CMFS does not support cluster, this patch only keeps 3 ML_ flags,
	ML_ERROR, ML_NOTICE, ML_KTHREAD.
In this patch, mlog_sys_init() & mlog_sys_shutdown() are not called by other code yet.