greybus: Rename gb_gpbridge_protocol_driver() as gb_builtin_protocol_driver()

This macro is also required by core protocols like control and svc, and
hence the 'gpbridge' name doesn't fit anymore.

Lets call this macro gb_builtin_protocol_driver().

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