dm: sandbox: pci: Add a PCI emulation uclass

Since sandbox does not have real devices (unless it borrows those from the
host) it must use emulations. Provide a uclass which permits PCI operations
to be passed through to an emulation device.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/pci/Makefile b/drivers/pci/Makefile
index 9e2e5f9..c1c2ae3c 100644
--- a/drivers/pci/Makefile
+++ b/drivers/pci/Makefile
@@ -8,6 +8,7 @@
 ifneq ($(CONFIG_DM_PCI),)
 obj-$(CONFIG_PCI) += pci-uclass.o pci_compat.o
 obj-$(CONFIG_PCI_SANDBOX) += pci_sandbox.o
+obj-$(CONFIG_SANDBOX) += pci-emul-uclass.o
 else
 obj-$(CONFIG_PCI) += pci.o
 endif