mips: Add arch/mips/include/asm/atomic.h

This is needed for the UBIFS support. The file is a copy of
arch/xtensa/include/asm/atomic.h

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>

arch/mips/include/asm/atomic.h

@@ -0,0 +1,54 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (C) 2016 Cadence Design Systems Inc.
+ */
+
+#ifndef _MIPS_ATOMIC_H
+#define _MIPS_ATOMIC_H
+
+#include <asm/system.h>
+
+typedef struct { volatile int counter; } atomic_t;
+
+#define ATOMIC_INIT(i)	{ (i) }
+
+#define atomic_read(v)		((v)->counter)
+#define atomic_set(v, i)	((v)->counter = (i))
+
+static inline void atomic_add(int i, atomic_t *v)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	v->counter += i;
+	local_irq_restore(flags);
+}
+
+static inline void atomic_sub(int i, atomic_t *v)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	v->counter -= i;
+	local_irq_restore(flags);
+}
+
+static inline void atomic_inc(atomic_t *v)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	++v->counter;
+	local_irq_restore(flags);
+}
+
+static inline void atomic_dec(atomic_t *v)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	--v->counter;
+	local_irq_restore(flags);
+}
+
+#endif