target-ppc: Fix an invalid free in opcode table handling code.

Opcode table has direct, indirect and double indirect handlers, but
ppc_cpu_unrealizefn() frees direct handlers which are never allocated
and never frees double indirect handlers.

Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
