net: mscc: Move miim commands into separate file.

Move miim functions that can be shared in a different file inside
mscc_eswitch.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
diff --git a/drivers/net/mscc_eswitch/mscc_miim.h b/drivers/net/mscc_eswitch/mscc_miim.h
new file mode 100644
index 0000000..0e5d5e3
--- /dev/null
+++ b/drivers/net/mscc_eswitch/mscc_miim.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: (GPL-2.0+ OR MIT) */
+/*
+ * Copyright (c) 2018 Microsemi Corporation
+ */
+
+struct mscc_miim_dev {
+	void __iomem *regs;
+	void __iomem *phy_regs;
+};
+
+int mscc_miim_read(struct mii_dev *bus, int addr, int devad, int reg);
+int mscc_miim_write(struct mii_dev *bus, int addr, int devad, int reg, u16 val);