include: Add lantiq.h in include/linux/

In some existing lantiq driver, the C codes include lantiq_soc.h
header file directly.

./arch/mips/include/asm/mach-lantiq/falcon/lantiq_soc.h
./arch/mips/include/asm/mach-lantiq/xway/lantiq_soc.h

Those drivers need to be extended to support more platform.
lantiq.h is added in include/linux/ to make it
globally available and provides some wrapper codes.
Signed-off-by: Songjun Wu <songjun.wu@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/lantiq.h

+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __LINUX_LANTIQ_H
+#define __LINUX_LANTIQ_H
+
+#ifdef CONFIG_LANTIQ
+#include <lantiq_soc.h>
+#else
+
+#ifndef LTQ_EARLY_ASC
+#define LTQ_EARLY_ASC 0
+#endif
+
+#ifndef CPHYSADDR
+#define CPHYSADDR(a) 0
+#endif
+
+static inline struct clk *clk_get_fpi(void)
+{
+	return NULL;
+}
+#endif /* CONFIG_LANTIQ */
+#endif /* __LINUX_LANTIQ_H */