PPC: KVM: Synchronize regs on CPU dump

When we dump the CPU registers, there's a certain chance they haven't been
synchronized with KVM yet, so we have to manually trigger that.

This aligns the code with x86 and fixes a bug where the register state was
bogus on invalid/unknown kvm exit reasons.

Reported-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
