KVM: PPC: RTAS: Do byte swaps explicitly

In commit b59d9d26 we introduced implicit byte swaps for RTAS calls.
Unfortunately we messed up and didn't swizzle return values properly.

Also the old approach wasn't "sparse" compatible - we were randomly
reading __be32 values on an LE system.

Let's just do all of the swizzling explicitly with byte swaps right
where values get used. That way we can at least catch bugs using sparse.

This patch fixes XICS RTAS emulation on little endian hosts for me.

Signed-off-by: Alexander Graf <agraf@suse.de>