target-ppc: Correct KVM synchronization for ppc_hash64_set_external_hpt()

ppc_hash64_set_external_hpt() was added in e5c0d3c "target-ppc: Add helpers
for updating a CPU's SDR1 and external HPT".  This helper contains a
cpu_synchronize_state() since it may need to push state back to KVM
afterwards.

This turns out to break things when it is used in the reset path, which is
the only current user.  It appears that kvm_vcpu_dirty is not being set
early in the reset path, so the cpu_synchronize_state() is clobbering state
set up by the early part of the cpu reset path with stale state from KVM.

This may require some changes to the generic cpu reset path to fix
properly, but as a short term fix we can just remove the
cpu_synchronize_state() from ppc_hash64_set_external_hpt(), and require any
non-reset path callers to do that manually.

Reported-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

target-ppc/mmu-hash64.c

@@ -284,8 +284,6 @@ void ppc_hash64_set_external_hpt(PowerPCCPU *cpu, void *hpt, int shift,
     CPUPPCState *env = &cpu->env;
     Error *local_err = NULL;
 
-    cpu_synchronize_state(CPU(cpu));
-
     if (hpt) {
         env->external_htab = hpt;
     } else {