greybus: manifest: Use interface descriptor instead of module descriptor to get information

A module can have more than one interfaces and we get hotplug events or
manifests for interfaces, not modules. Details like version, vendor,
product id, etc. can be different for different interfaces within the
same module and so shall be fetched from interface descriptor instead of
module descriptor.

So what we have been doing for module descriptors until now must be done
for interface descriptors. There can only be one interface descriptor in
the manifest. Module descriptor isn't used anymore and probably most of
its fields can be removed now.

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