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/powerpc/include/asm/scatterlist.h b/arch/powerpc/include/asm/scatterlist.h
index 4ae35da..34cc78f 100644
--- a/arch/powerpc/include/asm/scatterlist.h
+++ b/arch/powerpc/include/asm/scatterlist.h
@@ -15,5 +15,6 @@
 #ifdef __powerpc64__
 #define ISA_DMA_THRESHOLD	(~0UL)
 #endif
+#define ARCH_HAS_SG_CHAIN
 
 #endif /* _ASM_POWERPC_SCATTERLIST_H */