hw/pci/pci-stub: Add msi_enabled() and msi_notify() to the pci stubs

Some machines have an AHCI adapter, but no PCI. To be able to
compile hw/ide/ahci.c without CONFIG_PCI, we still need the two
functions msi_enabled() and msi_notify() for linking.
This is required for the new Kconfig-like build system, if a user
wants to compile a QEMU binary with just one machine that has AHCI,
but no PCI, like the ARM "cubieboard" for example.
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: NThomas Huth <thuth@redhat.com>

hw/pci/pci-stub.c

@@ -53,3 +53,14 @@ uint16_t pci_requester_id(PCIDevice *dev)
     g_assert(false);
     return 0;
 }
+
+/* Required by ahci.c */
+bool msi_enabled(const PCIDevice *dev)
+{
+    return false;
+}
+
+void msi_notify(PCIDevice *dev, unsigned int vector)
+{
+    g_assert_not_reached();
+}