KVM: PPC: Simplify kvmppc_load_up_(FPU|VMX|VSX)

We don't need as complex code. I had some thinkos while writing it, figuring
I needed to support PPC32 paths on PPC64 which would have required DR=0, but
everything just runs fine with DR=1.

So let's make the functions simple C call wrappers that reserve some space on
the stack for the respective functions to clobber.

Fixes out-of-RMA-access (and thus guest FPU loading) on the PS3.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>