mm: rust: add page.rs to MEMORY MANAGEMENT - RUST

The page.rs file currently isn't included anywhere, and I think it's a
good fit for the MEMORY MANAGEMENT - RUST entry.  The file was originally
added for use by Rust Binder, but I believe there is also work to use it
in the upcoming scatterlist abstractions.

Link: https://lkml.kernel.org/r/20250814075454.1596482-1-aliceryhl@google.com


Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>