fs: ceph: Initialize filesystem timestamp ranges

Fill in the appropriate limits to avoid inconsistencies
in the vfs cached inode times when timestamps are
outside the permitted range.

According to the disscussion in
https://patchwork.kernel.org/patch/8308691/

 we agreed to use
unsigned 32 bit timestamps on ceph.
Update the limits accordingly.

Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Acked-by: Jeff Layton <jlayton@kernel.org>
Cc: zyan@redhat.com
Cc: sage@redhat.com
Cc: idryomov@gmail.com
Cc: ceph-devel@vger.kernel.org