dt-bindings: add constants for Microsemi Ocelot SerDes driver

The Microsemi Ocelot has multiple SerDes and requires that the SerDes be
muxed accordingly to the hardware representation.

Let's add a constant for each SerDes available in the Microsemi Ocelot.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Quentin Schulz <quentin.schulz@bootlin.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/dt-bindings/phy/phy-ocelot-serdes.h

+/* SPDX-License-Identifier: (GPL-2.0 OR MIT) */
+/* Copyright (c) 2018 Microsemi Corporation */
+#ifndef __PHY_OCELOT_SERDES_H__
+#define __PHY_OCELOT_SERDES_H__
+
+#define SERDES1G(x)	(x)
+#define SERDES1G_MAX	SERDES1G(5)
+#define SERDES6G(x)	(SERDES1G_MAX + 1 + (x))
+#define SERDES6G_MAX	SERDES6G(2)
+#define SERDES_MAX	SERDES6G_MAX
+
+#endif