Drivers: hv: Support the newly introduced KVP messages in the driver

Support the newly defined KVP message types. It turns out that the host
pushes a set of standard key value pairs as soon as the guest opens the KVP channel.
Since we cannot handle these tuples until the user level daemon loads up, defer
reading the KVP channel until the user level daemon is launched.

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