hw/ppc/spapr: Test whether TCG is enabled with tcg_enabled()

hw/ppc/spapr: Test whether TCG is enabled with tcg_enabled()

Although the PPC target only supports the TCG and KVM
accelerators, QEMU supports more. We can not assume that
'!kvm == tcg', so test for the correct accelerator. This
also eases code review, because here we don't care about
KVM, we really want to test for TCG.

Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
[np: Fix changelog typo noticed by Zoltan]
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>