binder: use enum for binder ioctls

All of the other constants in this file are defined using enums, so make
the constants more consistent by defining the ioctls in an enum as well.

This is necessary for Rust Binder since the _IO macros are too
complicated for bindgen to see that they expand to integer constants.
Replacing the #defines with an enum forces bindgen to evaluate them
properly, which allows us to access them from Rust.

I originally intended to include this change in the first patch of the
Rust Binder patchset [1], but at plumbers Carlos Llamas told me that
this change has been discussed previously [2] and suggested that I send
it upstream separately.

Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-1-08ba9197f637@google.com/ [1]
Link: https://lore.kernel.org/all/YoIK2l6xbQMPGZHy@kroah.com/

 [2]
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Carlos Llamas <cmllamas@google.com>
Link: https://lore.kernel.org/r/20231208152801.3425772-1-aliceryhl@google.com


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