Ocfs2: Move ocfs2 ioctl definitions from ocfs2_fs.h to newly added ocfs2_ioctl.h

Currently we were adding ioctl cmds/structures for ocfs2 into ocfs2_fs.h
which was used for define ocfs2 on-disk layout. That sounds a little bit
confusing, and it may be quickly polluted espcially when growing the
ocfs2_info_request ioctls afterwards(it will grow i bet).

As a result, such OCFS2 IOCs do need to be placed somewhere other than
ocfs2_fs.h, a separated ocfs2_ioctl.h will be added to store such ioctl
structures and definitions which could also be used from userspace to
invoke ioctls call.

Signed-off-by: Tristan Ye <tristan.ye@oracle.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>