ARC: Provide a default serial.h for uart drivers needing BASE_BAUD

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/include/asm/serial.h

+/*
+ * Copyright (C) 2012 Synopsys, Inc. (www.synopsys.com)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef _ASM_ARC_SERIAL_H
+#define _ASM_ARC_SERIAL_H
+
+/*
+ * early-8250 requires BASE_BAUD to be defined and includes this header.
+ * We put in a typical value:
+ * 	(core clk / 16) - i.e. UART samples 16 times per sec.
+ * Athough in multi-platform-image this might not work, specially if the
+ * clk driving the UART is different.
+ * We can't use DeviceTree as this is typically for early serial.
+ */
+
+#include <asm/clk.h>
+
+#define BASE_BAUD	(arc_get_core_freq() / 16)
+
+#endif /* _ASM_ARC_SERIAL_H */