wan: ixp4xx_hss: prepare compile testing

The ixp4xx_hss driver needs the platform data definition and the
system clock rate to be compiled. Move both into a new platform_data
header file.

This is a prerequisite for compile testing, but turning on compile
testing requires further patches to isolate the SoC headers.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/platform_data/wan_ixp4xx_hss.h

@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PLATFORM_DATA_WAN_IXP4XX_HSS_H
+#define __PLATFORM_DATA_WAN_IXP4XX_HSS_H
+
+#include <linux/types.h>
+
+/* Information about built-in HSS (synchronous serial) interfaces */
+struct hss_plat_info {
+	int (*set_clock)(int port, unsigned int clock_type);
+	int (*open)(int port, void *pdev,
+		    void (*set_carrier_cb)(void *pdev, int carrier));
+	void (*close)(int port, void *pdev);
+	u8 txreadyq;
+	u32 timer_freq;
+};
+
+#endif