KVM: PPC: Add helper functions to call real mode loaders

Linux contains quite some bits of code to load FPU, Altivec and VSX lazily for
a task. It calls those bits in real mode, coming from an interrupt handler.

For KVM we better reuse those, so let's wrap a bit of trampoline magic around
them and then we can call them from normal module code.

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