Rename virt_smp_ops to psci_smp_ops and move them to arch/arm/kernel/psci_smp.c.
Remove mach-virt/platsmp.c, now unused.
Compile psci_smp if CONFIG_ARM_PSCI and CONFIG_SMP.
Add a cpu_die smp_op based on psci_ops.cpu_off.
Initialize PSCI before setting smp_ops in setup_arch.
If PSCI is available on the platform, prefer psci_smp_ops over the
platform smp_ops.