[SERIAL] Use an enum for serial8250 platform device IDs

Rather than hard-coding the platform device IDs, enumerate them.
We don't particularly care about the actual ID we get, just as
long as they're unique.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index d8a023d..317a979 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -30,6 +30,21 @@
 };
 
 /*
+ * Allocate 8250 platform device IDs.  Nothing is implied by
+ * the numbering here, except for the legacy entry being -1.
+ */
+enum {
+	PLAT8250_DEV_LEGACY = -1,
+	PLAT8250_DEV_PLATFORM,
+	PLAT8250_DEV_PLATFORM1,
+	PLAT8250_DEV_FOURPORT,
+	PLAT8250_DEV_ACCENT,
+	PLAT8250_DEV_BOCA,
+	PLAT8250_DEV_HUB6,
+	PLAT8250_DEV_MCA,
+};
+
+/*
  * This should be used by drivers which want to register
  * their own 8250 ports without registering their own
  * platform device.  Using these will make your driver