rust: sync: atomic: Add i8/i16 load and store support

rust: sync: atomic: Add i8/i16 load and store support

Add atomic operation support for i8 and i16 types using volatile
read/write and smp_load_acquire/smp_store_release helpers.

[boqun: Adjust [1] to avoid introduction of
impl_atomic_only_load_and_store_ops!() in the middle]

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Link: https://lore.kernel.org/all/20251228120546.1602275-1-fujita.tomonori@gmail.com/
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://patch.msgid.link/20251211113826.1299077-4-fujita.tomonori@gmail.com