asm-generic: remove ARCH_HAS_SG_CHAIN in scatterlist.h

There are more architectures that don't support ARCH_HAS_SG_CHAIN than
those that support it.  This removes removes ARCH_HAS_SG_CHAIN in
asm-generic/scatterlist.h and lets arhictectures to define it.

It's clearer than defining ARCH_HAS_SG_CHAIN asm-generic/scatterlist.h and
undefing it in arhictectures that don't support it.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/x86/include/asm/scatterlist.h b/arch/x86/include/asm/scatterlist.h
index 75af592..fb0b187 100644
--- a/arch/x86/include/asm/scatterlist.h
+++ b/arch/x86/include/asm/scatterlist.h
@@ -1,8 +1,9 @@
 #ifndef _ASM_X86_SCATTERLIST_H
 #define _ASM_X86_SCATTERLIST_H
 
-#define ISA_DMA_THRESHOLD (0x00ffffff)
-
 #include <asm-generic/scatterlist.h>
 
+#define ISA_DMA_THRESHOLD (0x00ffffff)
+#define ARCH_HAS_SG_CHAIN
+
 #endif /* _ASM_X86_SCATTERLIST_H */