ANDROID: binder: use 64-bit interface on 32-bit kernels.

There's no good reason to not use the 64-bit interface
on 32-bit kernels. Android userspace wants to support
generic 32-bit system images, and having to support two
binder interfaces on such a single image is practically
impossible.

Since the majority of deployed Android devices now run
a >= 4.4 userspace, this seems like a good time to flip
the default.

Change-Id: I01eedaf00546b681c3efe8e7880c53dca409675a
Signed-off-by: Martijn Coenen <maco@android.com>