atomic: cleanup asm-generic atomic*.h inclusion

After changing all consumers of atomics to include <linux/atomic.h>, we
ran into some compile time errors due to this dependency chain:

linux/atomic.h
  -> asm/atomic.h
    -> asm-generic/atomic-long.h

where atomic-long.h could use funcs defined later in linux/atomic.h
without a prototype.  This patches moves the code that includes
asm-generic/atomic*.h to linux/atomic.h.

Archs that need <asm-generic/atomic64.h> need to select
CONFIG_GENERIC_ATOMIC64 from now on (some of them used to include it
unconditionally).

Compile tested on i386 and x86_64 with allnoconfig.

Signed-off-by: Arun Sharma <asharma@fb.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: David Miller <davem@davemloft.net>
Acked-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/atomic.h b/include/linux/atomic.h
index d5e167a..42e7f63 100644
--- a/include/linux/atomic.h
+++ b/include/linux/atomic.h
@@ -96,4 +96,8 @@
 }
 #endif /* #ifndef CONFIG_ARCH_HAS_ATOMIC_OR */
 
+#include <asm-generic/atomic-long.h>
+#ifdef CONFIG_GENERIC_ATOMIC64
+#include <asm-generic/atomic64.h>
+#endif
 #endif /* _LINUX_ATOMIC_H */