aix: move and fix powerpc64 definitions into aix

move all type definitions and routine bindings into the aix top-level
module. the only supported target using aix is powerpc64. this has been
the case for some time. multiple existing definitions whose upstream
header conditionally uses different types for 32-bit and 64-bit machine
word sizes were already preferring the latter.

remove the aix/powerpc64 module. all bindings now live in the top-level
aix module.

fix some definitions. there were quite a few types that were either
declared with the wrong identifiers, were exposed as opaque types when
they're not upstream, or were otherwise only exposed in kernel mode.
existing sum types with conditionally compiled fields that rely on this
latter fact assume we are not compiling for that type of processes. this
assumption has transitively applied to the types brought over from the
powerpc64 submodule.

Author: dybucc