Staging: hv: vmbus: Show the modalias in /sys/bus/vmbus/devices/*/

Show a modalias file in /sys/bus/vmbus/devices/*/
Add a helper function to print the same content in modalias and uevent.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>