rename symbol: CONFIG_ORION5X -> CONFIG_ARCH_ORION5X

Have this symbol follow the pattern of all other such symbols.
This patch removes a TODO from the code.

Signed-off-by: Trevor Woerner <twoerner@gmail.com>
diff --git a/drivers/usb/host/Kconfig b/drivers/usb/host/Kconfig
index 2f381dc..cc9646d 100644
--- a/drivers/usb/host/Kconfig
+++ b/drivers/usb/host/Kconfig
@@ -135,7 +135,7 @@
 
 config USB_EHCI_MARVELL
 	bool "Support for Marvell on-chip EHCI USB controller"
-	depends on ARCH_MVEBU || KIRKWOOD || ORION5X
+	depends on ARCH_MVEBU || KIRKWOOD || ARCH_ORION5X
 	default y
 	---help---
 	  Enables support for the on-chip EHCI controller on MVEBU SoCs.