greybus: eliminate extra response flag definitions

All protocols use the same value to distinguish between request and
response message types.  This is a requirement.

Use GB_MESSAGE_TYPE_RESPONSE rather than GB_OPERATION_TYPE_RESPONSE
for the name of the flag used to distiguish between request and
response messages.

Get rid of the redundant response flag definitions that are
associated with specific protocols.

Describe the symbolic values as "operation types" rather than
"message types" where they are defined.  The message type for a
request is the same as the operation type; the message type for a
response is the operation type OR'd with GB_MESSAGE_TYPE_RESPONSE.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>