yaffs: set security attribute at file creation

Add support to yaffs to set the security attribute of new inodes when
they are created. This parallels similar support in other filesystems,
and is a requirement for SELinux and other MAC systems. This support
is used by SE Android, http://selinuxproject.org/page/SEAndroid.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Change-Id: I5139c6480be2ce535807e82e5914ac97973b669e