Staging: hv: enable mouse driver to build

But we disable it from automatically loading as that would
be bad.  This way people can build it easier and start cleaning
it up, as it needs it.

Cc: Hank Janssen <hjanssen@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>