KVM: PPC: Book3S: PR: Export kvmppc_copy_to|from_svcpu

The kvmppc_copy_{to,from}_svcpu functions are publically visible,
so we should also export them in a header for others C files to
consume.

So far we didn't need this because we only called it from asm code.
The next patch will introduce a C caller.

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