Staging: hv: rename the vmbus to "hyperv"

This changes the name of the bus in sysfs from "vmbus" to "hyperv" which
is the name it should show (vmbus is way to generic).

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