locking/atomic: microblaze: use asm-generic exclusively

Microblaze provides its own implementation of atomic_dec_if_positive(),
but nothing else. For a while now, the conditional inc/dec ops have been
optional, and the core code will provide generic implementations using
the code templates in scripts/atomic/fallbacks/.

For simplicity, and for consistency with the other conditional atomic
ops, let's drop the microblaze implementation of
atomic_dec_if_positive(), and use the generic implementation.

With that, we can also drop the local asm/atomic.h and asm/cmpxchg.h
headers, as asm-generic/atomic.h is mandatory-y, and we can pull in
asm-generic/cmpxchg.h via generic-y. This matches what nios2 and nds32
do today.

There should be no functional change as a result of this patch.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210525140232.53872-5-mark.rutland@arm.com

arch/microblaze/include/asm/Kbuild

 # SPDX-License-Identifier: GPL-2.0
 generated-y += syscall_table.h
+generic-y += cmpxchg.h
 generic-y += extable.h
 generic-y += kvm_para.h
 generic-y += mcs_spinlock.h

arch/microblaze/include/asm/atomic.h

-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _ASM_MICROBLAZE_ATOMIC_H
-#define _ASM_MICROBLAZE_ATOMIC_H
-
-#include <asm/cmpxchg.h>
-#include <asm-generic/atomic.h>
-#include <asm-generic/atomic64.h>
-
-/*
- * Atomically test *v and decrement if it is greater than 0.
- * The function returns the old value of *v minus 1.
- */
-static inline int atomic_dec_if_positive(atomic_t *v)
-{
-	unsigned long flags;
-	int res;
-
-	local_irq_save(flags);
-	res = v->counter - 1;
-	if (res >= 0)
-		v->counter = res;
-	local_irq_restore(flags);
-
-	return res;
-}
-#define atomic_dec_if_positive atomic_dec_if_positive
-
-#endif /* _ASM_MICROBLAZE_ATOMIC_H */

arch/microblaze/include/asm/cmpxchg.h

-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _ASM_MICROBLAZE_CMPXCHG_H
-#define _ASM_MICROBLAZE_CMPXCHG_H
-
-#ifndef CONFIG_SMP
-# include <asm-generic/cmpxchg.h>
-#endif
-
-#endif /* _ASM_MICROBLAZE_CMPXCHG_H */