nios2: Switch to generic __xchg()

The generic __xchg() implementation present in asm-generic/cmpxchg.h is
correct on nios2 and even generates the same code. Switch to this generic
implementation to trim down the amount of ad-hoc copies of the code.
Signed-off-by: Marek Vasut <marex@denx.de>
Acked-by: Ley Foon Tan <lftan@altera.com>

arch/nios2/include/asm/cmpxchg.h

@@ -9,53 +9,6 @@
 #ifndef _ASM_NIOS2_CMPXCHG_H
 #define _ASM_NIOS2_CMPXCHG_H
 
-#include <linux/irqflags.h>
-
-#define xchg(ptr, x)	\
-	((__typeof__(*(ptr)))__xchg((unsigned long)(x), (ptr), sizeof(*(ptr))))
-
-struct __xchg_dummy { unsigned long a[100]; };
-#define __xg(x)		((volatile struct __xchg_dummy *)(x))
-
-static inline unsigned long __xchg(unsigned long x, volatile void *ptr,
-					int size)
-{
-	unsigned long tmp, flags;
-
-	local_irq_save(flags);
-
-	switch (size) {
-	case 1:
-		__asm__ __volatile__(
-			"ldb	%0, %2\n"
-			"stb	%1, %2\n"
-			: "=&r" (tmp)
-			: "r" (x), "m" (*__xg(ptr))
-			: "memory");
-		break;
-	case 2:
-		__asm__ __volatile__(
-			"ldh	%0, %2\n"
-			"sth	%1, %2\n"
-			: "=&r" (tmp)
-			: "r" (x), "m" (*__xg(ptr))
-			: "memory");
-		break;
-	case 4:
-		__asm__ __volatile__(
-			"ldw	%0, %2\n"
-			"stw	%1, %2\n"
-			: "=&r" (tmp)
-			: "r" (x), "m" (*__xg(ptr))
-			: "memory");
-		break;
-	}
-
-	local_irq_restore(flags);
-	return tmp;
-}
-
 #include <asm-generic/cmpxchg.h>
-#include <asm-generic/cmpxchg-local.h>
 
 #endif /* _ASM_NIOS2_CMPXCHG_H */