greybus: add module support

Modules in the greybus system sit above the interface, so insert them
early in the sysfs tree.  We dynamically create them when we have an
interface that references a module, as we don't get a "module create"
message directly.  They also dynamically go away when the last interface
associated with a module is removed.

Naming scheme for modules/interfaces/bundles/connections is bumped up by
one ':', and now looks like the following:

/sys/bus/greybus $ tree
.
├── devices
│   ├── 7 -> ../../../devices/pci0000:00/0000:00:14.0/usb1/1-1/7
│   ├── 7:7 -> ../../../devices/pci0000:00/0000:00:14.0/usb1/1-1/7/7:7
│   ├── 7:7:0 -> ../../../devices/pci0000:00/0000:00:14.0/usb1/1-1/7/7:7/7:7:0
│   └── 7:7:0:1 -> ../../../devices/pci0000:00/0000:00:14.0/usb1/1-1/7/7:7/7:7:0/7:7:0:1
├── drivers
├── drivers_autoprobe
├── drivers_probe
└── uevent

6 directories, 3 files
/sys/bus/greybus $ grep . devices/*/uevent
devices/7/uevent:DEVTYPE=greybus_module
devices/7:7/uevent:DEVTYPE=greybus_interface
devices/7:7:0/uevent:DEVTYPE=greybus_bundle
devices/7:7:0:1/uevent:DEVTYPE=greybus_connection

We still have some "confusion" about interface ids and module ids, which
will be cleaned up later when the svc control protocol changes die down,
right now we just name a module after the interface as we don't have any
modules that have multiple interfaces in our systems.

This has been tested with gbsim.

Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>