KVM: PPC: Book3S HV: Fix build error when SMP=n

Commit 5d375199ea96 ("KVM: PPC: Book3S HV: Set server for passed-through
interrupts") broke the SMP=n build:

  arch/powerpc/kvm/book3s_hv_rm_xics.c:758:2: error: implicit declaration of function 'get_hard_smp_processor_id'

That is because we lost the implicit include of asm/smp.h, so include it
explicitly to get the definition for get_hard_smp_processor_id().

Fixes: 5d375199ea96 ("KVM: PPC: Book3S HV: Set server for passed-through interrupts")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kvm/book3s_hv_rm_xics.c

@@ -23,6 +23,7 @@
 #include <asm/ppc-opcode.h>
 #include <asm/pnv-pci.h>
 #include <asm/opal.h>
+#include <asm/smp.h>
 
 #include "book3s_xics.h"