greybus: operation: create gb_operation_sync for sending "simple" messages

Everyone keeps doing the same create/send/destroy logic all over the
place, so abstract that out to a simple function that can handle any
arbritrary request and/or response.  This will let us save lots of
duplicated logic in the protocol drivers.

Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>
Reviewed-by: Alex Elder <elder@linaro.org>