pci_ep: add pci endpoint sandbox driver

Add a dummy PCI endpoint for sandbox.
Supporting only a single function, it allows setting
and reading header configuration.

Signed-off-by: Ramon Fried <ramon.fried@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/dts/test.dts b/arch/sandbox/dts/test.dts
index c328258..a7a566c 100644
--- a/arch/sandbox/dts/test.dts
+++ b/arch/sandbox/dts/test.dts
@@ -487,6 +487,10 @@
 		};
 	};
 
+	pci_ep: pci_ep {
+		compatible = "sandbox,pci_ep";
+	};
+
 	probing {
 		compatible = "simple-bus";
 		test1 {