locking/barriers: Remove definitions for [smp_]read_barrier_depends()

There are no remaining users of [smp_]read_barrier_depends(), so
remove it from the generic implementation of 'barrier.h'.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>

include/asm-generic/barrier.h

@@ -46,10 +46,6 @@
 #define dma_wmb()	wmb()
 #endif
 
-#ifndef read_barrier_depends
-#define read_barrier_depends()		do { } while (0)
-#endif
-
 #ifndef __smp_mb
 #define __smp_mb()	mb()
 #endif
@@ -62,10 +58,6 @@
 #define __smp_wmb()	wmb()
 #endif
 
-#ifndef __smp_read_barrier_depends
-#define __smp_read_barrier_depends()	read_barrier_depends()
-#endif
-
 #ifdef CONFIG_SMP
 
 #ifndef smp_mb
@@ -80,10 +72,6 @@
 #define smp_wmb()	__smp_wmb()
 #endif
 
-#ifndef smp_read_barrier_depends
-#define smp_read_barrier_depends()	__smp_read_barrier_depends()
-#endif
-
 #else	/* !CONFIG_SMP */
 
 #ifndef smp_mb
@@ -98,10 +86,6 @@
 #define smp_wmb()	barrier()
 #endif
 
-#ifndef smp_read_barrier_depends
-#define smp_read_barrier_depends()	do { } while (0)
-#endif
-
 #endif	/* CONFIG_SMP */
 
 #ifndef __smp_store_mb
@@ -196,7 +180,6 @@ do {									\
 #define virt_mb() __smp_mb()
 #define virt_rmb() __smp_rmb()
 #define virt_wmb() __smp_wmb()
-#define virt_read_barrier_depends() __smp_read_barrier_depends()
 #define virt_store_mb(var, value) __smp_store_mb(var, value)
 #define virt_mb__before_atomic() __smp_mb__before_atomic()
 #define virt_mb__after_atomic()	__smp_mb__after_atomic()