rust: add rcu abstraction

Add a simple abstraction to guard critical code sections with an rcu
read lock.

Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
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>
Tested-by: Fabien Parent <fabien.parent@linaro.org>
Link: https://lore.kernel.org/r/20241219170425.12036-5-dakr@kernel.org


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