ppc/pef.c: initialize cgs->ready in kvmppc_svm_init()

ppc/pef.c: initialize cgs->ready in kvmppc_svm_init()

QEMU is failing to launch a CGS pSeries guest in a host that has PEF
support:

qemu-system-ppc64: ../softmmu/vl.c:2585: qemu_machine_creation_done: Assertion `machine->cgs->ready' failed.
Aborted

This is happening because we're not setting the cgs->ready flag that is
asserted in qemu_machine_creation_done() during machine start.

cgs->ready is set in s390_pv_kvm_init() and sev_kvm_init(). Let's set it
in kvmppc_svm_init() as well.

Reported-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20210528201619.52363-1-danielhb413@gmail.com>
Acked-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>