drivers: hv: kvp: Cleanup the kernel/user protocol

Now, cleanup the user/kernel KVP protocol by using the same structure
definition that is used for host/guest KVP protocol. This simplifies the code.

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