rust: bitmap: add MAX_LEN and MAX_INLINE_LEN constants

rust: bitmap: add MAX_LEN and MAX_INLINE_LEN constants

To avoid hard-coding these values in drivers, define constants for them
that drivers can reference. Also, update all instances in bitmap.rs and
id_pool.rs that use these values to use the new constants.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Burak Emir <bqe@google.com>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>