hv: use dev_groups for device attributes

This patch is the first in a series that moves the hv bus code to use the
dev_groups field instead of dev_attrs, as dev_attrs is going away in future
kernel releases.

It moves the id sysfs file to the dev_groups structure, and creates the needed
show/store functions, instead of relying on one "universal" function for this.
By doing this, it removes the need for this to be in a temporary structure.

Tested-by: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/hyperv.h

@@ -900,7 +900,6 @@ enum vmbus_channel_state {
 };
 
 struct vmbus_channel_debug_info {
-	u32 relid;
 	enum vmbus_channel_state state;
 	uuid_le interfacetype;
 	uuid_le interface_instance;