KVM: PPC: Add MMIO emulation for stdx (store doubleword indexed)

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>

arch/powerpc/include/asm/ppc-opcode.h

@@ -94,6 +94,7 @@
 #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

arch/powerpc/kvm/emulate_loadstore.c

@@ -119,6 +119,12 @@ int kvmppc_emulate_loadstore(struct kvm_vcpu *vcpu)
 			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),