Staging: hv: remove vmbus.c

Merge the functions into vmbus_drv.c as there's no need to have them
separate anymore.  It will also make unwinding some of the function and
pointer mess easier, as well as making functions static in the future.

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