KVM: PPC: Move of include to __KERNEL__ section

We have to protect the include for linux/of.h by __KERNEL__ so it doesn't
accidently get referenced outside.

This patch fixes this and makes the tree compile again.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Alexander Graf <agraf@suse.de>