greybus: interface_block: s/gb_module/gb_interface_block/

Rename struct gb_module to struct gb_interface_block

It's a complex rename, some functions got their name changed where
needed, but primarily this change is focused on the structure and where
it is used.  Future changes will clean up the remaining usages of the
term "module" in individual changes, this one spanned the whole
subsystem so do it all at once.

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