[build] Add named configuration for Raspberry Pi

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/config/rpi/usb.h

@@ -0,0 +1,13 @@
+/*
+ * Use EFI_USB_IO_PROTOCOL
+ *
+ * The Raspberry Pi uses an embedded DesignWare USB controller for
+ * which we do not have a native driver.  Use via the
+ * EFI_USB_IO_PROTOCOL driver instead.
+ *
+ */
+#undef USB_HCD_XHCI
+#undef USB_HCD_EHCI
+#undef USB_HCD_UHCI
+#define USB_HCD_USBIO
+#undef USB_EFI