rust: add `Revocable` type

Revocable allows access to objects to be safely revoked at run time.

This is useful, for example, for resources allocated during device probe;
when the device is removed, the driver should stop accessing the device
resources even if another state is kept in memory due to existing
references (i.e., device context data is ref-counted and has a non-zero
refcount after removal of the device).

Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
Co-developed-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Tested-by: Dirk Behme <dirk.behme@de.bosch.com>
Link: https://lore.kernel.org/r/20241219170425.12036-7-dakr@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>