greybus: greybus_protocols: add missing version-request definition

Add the missing version-request definition that was falsely claimed to
be empty.

Update the generic version-request helper and SVC version-request
handler to use the request definition rather than rely on the response
happening to have the same layout, something which also improves
readability.

Remove a misplaced "Control Protocol" header while at it.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>