greybus: constify the struct device_type usage

Since commit aed65af1cc2f ("drivers: make device_type const"), the driver
core can properly handle constant struct device_type. Move the
greybus_hd_type, greybus_module_type, greybus_interface_type,
greybus_control_type, greybus_bundle_type and greybus_svc_type variables to
be constant structures as well, placing it into read-only memory which can
not be modified at runtime.

Signed-off-by: "Ricardo B. Marliere" <ricardo@marliere.net>
Reviewed-by: Alex Elder <elder@linaro.org>
Link: https://lore.kernel.org/r/20240219-device_cleanup-greybus-v1-1-babb3f65e8cc@marliere.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

staging: greybus: move the greybus core to drivers/greybus

The Greybus core code has been stable for a long time, and has been
shipping for many years in millions of phones. With the advent of a
recent Google Summer of Code project, and a number of new devices in the
works from various companies, it is time to get the core greybus code
out of staging as it really is going to be with us for a while.

Cc: Johan Hovold <johan@kernel.org>
Cc: linux-kernel@vger.kernel.org
Cc: greybus-dev@lists.linaro.org
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Alex Elder <elder@kernel.org>
Link: https://lore.kernel.org/r/20190825055429.18547-9-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>