This adds missing stdx emulation for emulated MMIO accesses by KVM
guests.  This allows the Mellanox mlx5_core driver from recent kernels
to work when MMIO emulation is enforced by userspace.
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
 #define OP_31_XOP_TRAP_64   68
 #define OP_31_XOP_DCBF      86
 #define OP_31_XOP_LBZX      87
+#define OP_31_XOP_STDX      149
 #define OP_31_XOP_STWX      151
 #define OP_31_XOP_STBX      215
 #define OP_31_XOP_LBZUX     119
 
                        kvmppc_set_gpr(vcpu, ra, vcpu->arch.vaddr_accessed);
                        break;
 
+               case OP_31_XOP_STDX:
+                       emulated = kvmppc_handle_store(run, vcpu,
+                                                      kvmppc_get_gpr(vcpu, rs),
+                                                       8, 1);
+                       break;
+
                case OP_31_XOP_STWX:
                        emulated = kvmppc_handle_store(run, vcpu,
                                                       kvmppc_get_gpr(vcpu, rs),