KVM: PPC: Assembly functions exported to modules need _GLOBAL_TOC()

Both kvmppc_hv_entry_trampoline and kvmppc_entry_trampoline are
assembly functions that are exported to modules and also require
a valid r2.

As such we need to use _GLOBAL_TOC so we provide a global entry
point that establishes the TOC (r2).

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>