kvm tools: powerpc: Fix init order for xics

xics_init() assumes kvm->nrcpus is already setup.  kvm->nrcpus is setup
in kvm_cpu_init()

Unfortunately xics_init() and kvm_cpu_init() both use base_init().  So
depending on the order randomly determined by the compiler, xics_init()
may initialised see kvm->nrcpus as 0 and not setup any of the icp VCPU
pointers.  This manifests itself later in boot when trying to raise an
IRQ resulting in a null pointer deference/segv.

This moves xics_init() to use dev_base_init() to ensure it happens after
kvm_cpu_init().

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Pekka Enberg <penberg@kernel.org>