PPC32: make xchg take volatile *, remove duplicate xchg_u32 defn.

Previously we had xchg_u32 both inline in system.h and out-of-line
in arch/ppc/kernel/misc.S, and it was exported for good measure.
We only need the inline definition.

arch/ppc/kernel/misc.S

@@ -751,21 +751,6 @@ _GLOBAL(copy_page)
 	blr
 #endif /* CONFIG_PPC_ISERIES */
 
-/*
- * Atomic [test&set] exchange
- *
- *	unsigned long xchg_u32(void *ptr, unsigned long val)
- * Changes the memory location '*ptr' to be val and returns
- * the previous value stored there.
- */
-_GLOBAL(xchg_u32)
-	mr	r5,r3		/* Save pointer */
-10:	lwarx	r3,0,r5		/* Fetch old value & reserve */
-	PPC405_ERR77(0,r5)
-	stwcx.	r4,0,r5		/* Update with new value */
-	bne-	10b		/* Retry if "reservation" (i.e. lock) lost */
-	blr
-
 /*
  * void atomic_clear_mask(atomic_t mask, atomic_t *addr)
  * void atomic_set_mask(atomic_t mask, atomic_t *addr);

arch/ppc/kernel/ppc_ksyms.c

@@ -191,7 +191,6 @@ EXPORT_SYMBOL(flush_dcache_range);
 EXPORT_SYMBOL(flush_icache_user_range);
 EXPORT_SYMBOL(flush_icache_page);
 EXPORT_SYMBOL(flush_dcache_page);
-EXPORT_SYMBOL(xchg_u32);
 #ifdef CONFIG_ALTIVEC
 EXPORT_SYMBOL(last_task_used_altivec);
 EXPORT_SYMBOL(giveup_altivec);

include/asm-ppc/system.h

@@ -119,14 +119,14 @@ extern void __xchg_called_with_bad_pointer(void);
 #define xchg(ptr,x) ((__typeof__(*(ptr)))__xchg((unsigned long)(x),(ptr),sizeof(*(ptr))))
 #define tas(ptr) (xchg((ptr),1))
 
-static inline unsigned long __xchg(unsigned long x, void * ptr, int size)
+static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size)
 {
 	switch (size) {
 	case 4:
-		return (unsigned long )xchg_u32(ptr, x);
+		return (unsigned long) xchg_u32(ptr, x);
 #if 0	/* xchg_u64 doesn't exist on 32-bit PPC */
 	case 8:
-		return (unsigned long )xchg_u64(ptr, x);
+		return (unsigned long) xchg_u64(ptr, x);
 #endif /* 0 */
 	}
 	__xchg_called_with_bad_pointer();