x86: Export the symbol ms_hyperv

This is needed so that the staging hyperv can properly access this
symbol.

Signed-off-by: K. Y. Srinivasan <ksrinivasan@novell.com>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>