Staging: hv: remove duplicated osd.o inclusions

Now that we have properly prefixed the osd.c functions, we don't need to
include it in each of the modules.  So only build it into the hv_vmbus
module.

Export the symbols that the other hv_ modules need, so that they can
properly find them.

Cc: Bill Pemberton <wfp5p@virginia.edu>
Cc: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>