greybus: drop gb_* device fields from gb_module

A struct gb_module has a bunch of fields from the earlier skeleton
code, where a module was assumed to possibly have one of every
type of device available on the GP Bridge.  The manifest parsing
code changed it so these things will be related to connection
endpoints, so these gb_module fields are no longer needed.

A few of these (battery and sdio) haven't been implemented the "new
way" yet, so just leave a bit of the code that was there commented
out for now.

Also, gb_tty seems to be partially implemented and I don't want to
remove that without knowing where it's headed, so that one stays.

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