rust: driver: decouple driver private data from driver type

rust: driver: decouple driver private data from driver type

Add a type Data<'bound> associated type to all bus driver traits,
decoupling the driver's bus device private data type from the driver
struct itself.

In the context of adding a 'bound lifetime, making this an associated
type has the advantage that it allows us to avoid a driver trait global
lifetime and it avoids the need for ForLt for bus device private data;
both of which make the subsequent implementation by buses much simpler.

All existing drivers and doc examples set type Data = Self to preserve
the current behavior.

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/20260525202921.124698-5-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>