vexpress64: compile Juno PCIe conditionally

Only compile in PCIe support if the board really uses it. Provide
a __weak stub for the init function if e.g. FVP is being built.

Signed-off-by: Ryan Harkin <ryan.harkin@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/board/armltd/vexpress64/vexpress64.c b/board/armltd/vexpress64/vexpress64.c
index f4e8084..3add099 100644
--- a/board/armltd/vexpress64/vexpress64.c
+++ b/board/armltd/vexpress64/vexpress64.c
@@ -28,6 +28,13 @@
 	.platdata = &serial_platdata,
 };
 
+/* This function gets replaced by platforms supporting PCIe.
+ * The replacement function, eg. on Juno, initialises the PCIe bus.
+ */
+__weak void vexpress64_pcie_init(void)
+{
+}
+
 int board_init(void)
 {
 	vexpress64_pcie_init();