greybus: move methods into protocol

greybus: move methods into protocol

Get rid of the connection handler structure, and instead put the
methods that were there into the protocol structure.

Eliminate the big switch statement in connection_init() and just
call the connection's protocol's init function there directly.

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