arm/arm64: KVM: Statically configure the host's view of MPIDR

We currently eagerly save/restore MPIDR. It turns out to be
slightly pointless:
- On the host, this value is known as soon as we're scheduled on a
  physical CPU
- In the guest, this value cannot change, as it is set by KVM
  (and this is a read-only register)

The result of the above is that we can perfectly avoid the eager
saving of MPIDR_EL1, and only keep the restore. We just have
to setup the host contexts appropriately at boot time.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>

virt/kvm/arm/arm.c

@@ -1561,6 +1561,7 @@ static int init_hyp_mode(void)
 		kvm_cpu_context_t *cpu_ctxt;
 
 		cpu_ctxt = per_cpu_ptr(&kvm_host_cpu_state, cpu);
+		kvm_init_host_cpu_context(cpu_ctxt, cpu);
 		err = create_hyp_mappings(cpu_ctxt, cpu_ctxt + 1, PAGE_HYP);
 
 		if (err) {