Move the 64-bit overlay structures to the utmath module since
they are used nowhere else. Update module comment. ACPICA BZ 829.

http://www.acpica.org/bugzilla/show_bug.cgi?id=829Signed-off-by: NBob Moore <robert.moore@intel.com>
Signed-off-by: NLin Ming <ming.m.lin@intel.com>
Signed-off-by: NLen Brown <len.brown@intel.com>